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yes
but why the background radiation?
because no matter how much the isotope decays, the background will still contribute the same amount of counts to the detector
ok so i shud add the background radiation to every calculation like this?
total counts = [ counts from isotope that decays and will decrease] + [ counts from background that doesn't change]
ok ty
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i understand how to solve this problem execpt i don't understand what they mean by roots in math
The root of function is where y =0
oh
So the root of y = x-1 is x=1
Roots are basically the answers
Yea
Do you know how to split the middle term here?
yes i think its 3(-x^2+3x+18)
Well that's the first step
Next you need to split 3x into 2 terms
Whose sum is 3x and product is -18
(blank)(blank)?
Yea this will be the final answer
oh i can do that
for the root or the factored equation?
factored equation
k
Yea
then you can equate the (blank) to 0 to get roots
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hi bum lol
,calc 46 * 7
Result:
322
vector word questions
why were they the hardest thing in my life
it was the plane and boat ones
one worth 8 marks one worth 12 marks
so if u got one thing at the start wrong u basically fumbled the whole question
they’re gonna be in my end of year exam too 😭
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To find phase shift of a cosine graph do you see the horizontal distance from x = 0?
pretty much
like the max?
so if the min is on x = 0 and the max is on x = 1 the phase shift is 1?
<@&286206848099549185>
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i don't understand how you would come to this solution
the answer i came to was:
-(1/4x - 2)^3
yeah
Stretch is to expand the thing right ?
yeah
What happens if u expand the thing by 0.25 its original size?
ok so you would put 1/4 if they said horizontally compress by a factor of 4
gets smaller
ok
Then
but why is it 4x-8
-4x^3 to get vertical reflection
you have to distribute that to the -2 as well?
Substitute x-2 into x to move the thing by 2
oh so c might not always be what it appears like
Ja
bc you have to distribute sometimes
ok that makes more sense
is there an easier way to memorize this compression and stretch stuff
Yes
When multiply something > 1, what do u think will happen to the rate of change of the functions?
Or the slope in general
goes up
It goes faster
yep
oh that makes more sense
Apply the same logic for stretching
👍
that's why it's vertical stretch and it's the opposite for horizontal bc horizontal stretch would make it slower
ty this is actually really helpful
Glad it helps 👍🥹
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A drug company produces pills containing an active ingredient. The company is
concerned about the mean weight of this ingredient per pill, but it also requires that the variance (in
squared milligrams) be no more than 1.5. A random sample of twenty pills is selected, and the sample
variance is found to be 2.05 . What is the probability that a sample variance this high or higher would
be found if the population variance is in fact 1.5? Assume that the population distribituion is normal
This is what I have done so far:
$\frac{(n-1)S^2}{\sigma^2}$, where $n = 20, S^2 = 2.05, \sigma^2 = 1.5$.
$\frac{19 \cdot 2.05}{1.5} = 25.9666 \approx 25.97$
We need to find $P(\chi_{19}^2 >= 25.97)$
Using the table it would be $0.1 < P(\chi_{19}^2 >= 25.97) < 0.9$ ?
Calc III Victim
Idk how to find the exact value for $P(\chi_{19}^2 >= 25.97)$
Calc III Victim
and (0.1, 0.9) seems like a crazy interval so idk if im doing this properly
Where does that come from?
Use software (for example in R type 1-pchisq(25.97, 19)) or look at a table
This is a past midterm question im pretty sure they werent allowed to use R. but ye I was looking at the table and 25.97 seems to be between 0.1 and 0.9 for df 19
You can only approximate it then
also why would it be 1 - pchisq for P(chi_19 > 25.97)? wont it be 1 - pchisq if it was P(chi_19 < 25.97)?
so would 0.1 < P < 0.9 be good enough?
p…(q,…) finds P(…<=q) for any implemented distribution in R
ah I see
You want P(…>=q) so the complement (since continious this works)
I would imagine they expect smth like linear interpolation then
But dk
whats that? never heard of it before
A quick hand wavy estimate is from P(…)=0.9 to P(…)=0.95 it goes from 27 to 30. So linear interpolation the other way gives P(…)=0.85 would correspond to 24 ish. We want at 26 so like 0.88 is a reasonable approx
Basically you assume its linear in the interval to do approximation using change of near points
(The correct answer is 0.87 so fairly close)
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I’m new to implicit differentiation can someone explain why is this wrong
Ok
It’s
x^2y’ + 2xy - 2ayy’ = 0
2xy = 2ayy’ - x^2y’
2xy(2ay - x^2) = y’
Also
U forgot the negative sign factoring
Which line is this?
2 -> 3
Also, I’m not sure whether the answer u get is similar to mine
Cuz it is hard to rearrange
Nvm
Your answer = 2xy^2 / (ay^2 - x^2y + ay^2)
= 2xy^2 / (2ay^2 - x^2y)
= 2xy / (2ay - x^2)
Sorry I gtg will look at it ltr thx 🙏
Oh
a weird thing you did is divide by y, you dont need to divide the whole eq by y, youll get the answer easier
U made two mistakes
But they correct each other
Miraculously 😭
In line 2 -> 3, u forgot to bring the negative after the differentiation out and also factored out dy/dx out without considering the sign
But they cancelled
So u have a correct answer
@stoic nimbus
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Can someone help me with q12?
Induction proof will work
Fr
But do u know sum of binomial coefficients from r=1 to n is 2^n -1
This is the hint
For real
I got it
How to explain him
Fr
@knotty flume
U know gp?
Gp
?
By gp u mean geometric progression?
Yes
Write the sum
(2^n - 1)
Now did u get the hint
Ohhhh
Thanks
Am gm
Nice
First person to literally understand the fastest
Teacher isint ready for this
Bros a fast learner
I got this idea of gp bcz below weighted means it is written fr 🔥 
Bro is studying progression and series
Ye
Fr fr 🗣️🙊
Poor teacher doing induction while 2pages and you came with those 4 lines up
Got u
Oppailol are u in hs?
hs?
Highschool
Ohoh
We in same hs in discord
Lol fr 🔥🗣️
We might not be in same hs but we in same zone fr 🔥🗣️
Highschool 
Ooh
The good ol' days
Fr bro fr
I wish I was back in high school
But it just gets harder 
Fr 🔥
Wait until you hear that you do triple integrals in college
So many languages but chose to speak fax 🗣️
Final oral exam in hs was on it
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Welcome from the side of everyone who helped
Imma go now bye
@clear cloud @ocean onyx cya

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how to solve thissss
should i expand it?
i dont think so
recall the range of sinx and cosx
which is from -1 to 1 inclusive
ohh thank you i get it
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I would like to prove the convergence of the sequence with the Cauchy criterion, how can I get rid of the plus one in my calculation? Or how should I have calculated differently?
In the last row, why estimate it like that?
If you have (1+n)/n^2
Then why not use that?
For example you could estimate 1+n like 2n for big n
If you want it neater
Ah yes 1 + n <= 2n is genius
Ur welcome aha
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why? how can visulize it?
what exactly do you mean with visualize
@fresh pendant Has your question been resolved?
the wikipedia article on radius of convergence has some examples of functions where it converges for some z and diverges for some other z with |z-a|=R
I mean, like this:
Am i understanding it correctly?
ye so what should it be like
in the interval (a-R, a+R) it converges
at the points a-R and a+R it may or may not converges
it's said in the pic but it's hard for me to visualize it correctly
I have no clue what you are thinking to get that picture
are you mixing it up with the epsilon-N definition of convergence of a sequence?
I mean thats related I suppose but not really helpful
no, it's just inconvinient to plot it with discrete pionts so i used line
but what are you trying to plot
Trying to understand
you have a series $\sum a_n z^n$, yes?
Denascite
and into the z you are plugging in different values
so for example you might to try to plug in $z=2$ which would give you $\sum a_n 2^n$
Denascite
or you might want to plug in $z=-1$ and get $\sum a_n (-1)^n$
Denascite
or $z=17$ which would give you $\sum a_n 17^n$
Denascite
all of these are different series
they might converge or they might not
the radius of convergence tells you for which z it converges
can this sequence be an example
@fresh pendant Has your question been resolved?
well take the series $\sum (-1)^nz^n$ for example then
rafilou2003
radius of convergence is 1
and for |z| < 1, it converges to 1/(1+z)
but if you take |z| = 1, in this example it's impossible for the series to converge
since |(-1)^nz^n| = 1 which doesn't converge to 0
so the series doesn't converge on any point of the boundary
another example : a_n = 1/n
becomes the series $\sum \frac{z^n}{n}$
rafilou2003
radius of convergence is again 1
but here if |z| = 1, the series may or may not converge
if z = 1 then $\sum \frac{1}{n}$ diverges, harmonic series
rafilou2003
if $z = -1$ then $\sum \frac{(-1)^n}{n}$ converges, alternating series
rafilou2003
so it depends
@fresh pendant depending on a_n, the series may or may not converge depending on which point of the edge of the disk of convergence we're looking at
ok so basically The radius of convergence R is the distance within which the series converges. For ∣z∣<R, the series converges, and for ∣z∣>R, the series diverges. On the boundary ∣z∣=R, the behavior of the series can vary—it may converge at some points and diverge at others?
exactly
note that what you wrote is for a power series centered at 0
$\sum a_n z^n$ specifically
rafilou2003
for a series centered at a point $a$, it's gonna be $\sum a_n (z-a)^n$
rafilou2003
and in this case the radius of convergence is "what is the MAX distance possible can you go from point a and still hope to converge"
because if you go further than R, meaning |z-a| > R, it diverges
meanwhile if |z-a| < R it always converges
so |z-a| = R are the cases we don't know about
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is f(x) = xsin(1/x) continuous on [0,1] ?
f is not defined for x=0 so i am a bit confused by this question
I don’t think a function can be continuous at a point it’s not even defined at 
im confused by point c
theorem 4.4.7 states that if a function is continuous on a compact set K then it is uniformly continuous on K
(0,1), not [0,1]
yes but the solution says that it is continuous over [0,1]
more precisely, it can be continuously extended to x=0
define f(0)=0
what does this mean?
there is a function g(x) such that g(x)=f(x) for all x in (0,1) and g is defined on [0,1] and g is continuous
@gaunt temple Has your question been resolved?
so if f(x) = xsin(1/x) is continuous at (0,1] then i can extend the continuity over [0,1] by making a new function g(x) defined as g(x) = xsin(1/x) for x in (0,1] and g(x) = 0 for x=0 ?
and this can be done because 0 is an accumulation point, i.e. lim x-->0 f(x) = 0
conversely, a function like f(x) = 1/x can't be extended to be continuous at 0 because there's a vertical asymptote at x=0 and x is not an accumulation point
so h(x) is not continuous at [0,1] because it is not defined at 0, but if we make a new function m defined as m(x) = xsin(1/x) if x is in (0,1] and m(x) = 0 if x = 0, then m is continuous
correct?
yes
but then we dont often care to explicitly mention all that stuff, so we just say that h itself is continuous
with the implicit understanding that we actually do this entire construction
okay thanks very much 🙂
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Im rly confused here
the mark scheme says to work out the interquartile rang and whatever
and Ik how to do that ez
but idk why am I doing it
@subtle ether Has your question been resolved?
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the question is
what I don’t understand is
why is this person
using the first derivative
isnt the first derivative to find the gradient?
stationary point is when the first derivative is 0
I see
ty
so essentially
first derivative
- related to gradient
when dy/dx = 0, this is stationary
second derivative - related to nature of stationary point
d2y/dx2 > 0, minimum
d2y/dx2 < 0, maximum
second derivative is related to concavity
i.e. concave up or down
or inflection point
You can’t decide if a point is a stationary point or not just by using the second derivative
You need the n’th derivative test for that
is this correct?
let me check what this is
ik
by those 3
I shortened it into “nature”
that’s the term my teacher uses
this isn’t within my syllabus
but I see
ty
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how do i find the equation of a reciprocal graph?
@young minnow Has your question been resolved?
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Here, if x = 4, then thats 1/-1 which is = -1 right? so how is it the case as shown for x > 3 is 1 please?
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I know that the integral is going to be from 0 to 1 at the beginning
from there on I don't where to go from
do you know how to find the volume of a revolution around the x-axis?
yes
so it’s basically the same, except you integrate in terms of y
so instead of dx, it’s dy
otherwise it’s the exact same
So like this
don’t forget to multiply by pi
and you forgot a parentheses at the end
before the squared
but other yea that’s good
And the sqaure goes to everything making it 4tan^2(pi/3y)
My notes didn't include tan so that's why I'm having difficulty
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hello so I was wondering if this formula would hold if instead of cos x it's cos(x + constant) and sin x is sin (x + constant)?
is it the same constant?
Yes
then yes
okay
I have another question
A question asked for the period of 1/2 cos(2t) + 1/4sin(t) + 3. Idk how to do this is there like some similar formula I can do to make the trig one function or something
@wraith hinge Has your question been resolved?
@wraith hinge Has your question been resolved?
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1+2=3 1/3=a???
is a always just a 1 or -1
Think about it like 2 -1/3 |x+3|
As x gets closer to -3 the function gets closer to 2
Because ur subtracting less and less
After x= -3
You start subtracting more and more
So it increases and then decreases
If it was 1/3 | x+3 | +2 then jt would be the oposite
You would be adding less and less until x=-3
And then start adding more and more
so i wouldnt solve for a I would just see if its positive or negative?
or is a the slope
@winged solar Has your question been resolved?
how did you get 2(x-1)
and then?
y = 0 so thats it
I used my slope for a
what formula are you applying to get the final equation
state the formula
2(x+1)
yes
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Why is this not64x^4 because 16/4 is 4 but 256/4 is 64 no?
You're doing 256^(1/4) not 256/4
With values, you're taking that root
So the 4th root of 256
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you can find what AD is equal to and therefore what OD is
cause its a parallelogram AD and BC should be equal
thats also right tho
oh crap did I just make algebra mistakes then
wait, idk if im getting direction correct cause im just looking at this
Add directional vector BC to position vector A
ABCD form a parallelogram
We just know the position of A,B,C,D with respect to O origin
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Which point in a tetrahedron has the minimum total distance to the vertices of the tetrahedron?
i.e. P in tetrahedron ABCD with minimal AP+BP+CP+DP
you can find it easily,
show what you have tried
this is for disphenoids
one way to do it first find in a triangle, then extend it to the line perpendicular to it, then differentiate to find minima
and if you know thedefinition of centroid
you can do it quickly
Fermat point?
yeah
What if I find the Fermat points of each face and connect the perpendiculars
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can someone please help me solve this (sorry if i am not supposed to be posting here its just confusing on where to post my questions)
i have tried changing to sin2x/cos2x
but im still ocnfused on what to do
and then i tried multiplying cos2x on both sides to get sin2x by itself
idk if thats right
its fine, but unnecessary
if you know how to work with tan
do you know how to solve
sin(2x) = 0
do you know how to solve sin(x) = 0
Yo i came
and my answer was 0, 180 and 360
ok.
so instead of getting
x = ...
directly
for sin(2x) = 0,
you'll have
2x = ...
then divide everything by 2 to get x
i seee
what do i do with the tan tho since it equals 0 do i find any quadrants or something
ik what to do if its neg or pos but what if it = 0 what happens then
tan(x) is 0 in the same place sin(x) is 0
yeh
okay
the work you did leads to
sin(2x) = 0
See inactive
okay
yes
no
😓
how do i figure that out
im generally strugglign with any of these types of questions ending with = 0
and with '2'x but im starting to understand the 2
$\sin(x) = 0\
\sin(\this) = 0$
ℝαμΩℕωⅤ
list the solutions for "this"
they'd be the same as the solutions for the original x
for sinx=0 i looked at a unit circle
so if i try solving without the unit circle
how do i do it
know special angles, and periodicity of the trig functions
unit circle definitions of trig functions
sin(t) gives the y-coord of the point on the unit circle at angle t
first list the angles at when
sin(this) = 0
'this' here just happens to be 2x
this next step very similar to what you'd do when solving sin(x) = 0
you've already identified that
sin(x) = 0
when x= stuff like 0,180,360
so sin(2x) will equal 0 when
2x = stuff like 0,180,360
(or their radians equivalent)
however note that since you're being asked for solutions of x in [0,2pi], you'd need to consider values where 2x is in [0,4pi] or [0,720°]
so you'd need a few more values
@outer vector Has your question been resolved?
i seeeee
so 2 revolutions
if it = 0
do i consider using quadrants or no
like for anything > 0 i find quads but when it = 0
do i still use quads
angles on the axis aren't considered to be part of quadrants
consider periodicity and what you observed from looking at the unit circle
yes
so pi, 2pi, 3pi, 4pi
0 as well
Indeed, you haven't solved it yet
Your answers are in terms of 2x so far
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i dont undertsand this
Do you understand what a reciprocal function is?
Do u understand what is a reciprocal?
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how did they solve for phi here?
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How would you find phi in this case?
I got cot(phi) = sqrt(5)
but Im not sure how to solve for phi
with the basic unit circle
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derivative of 2x^3 - 6x^2 > 0
2x^3 - 6x^2 > 0
6x^2 - 12x > 0
(6x)(x - 2) > 0
I know im supposed to get an answer x> something and x< something right?
I don’t know if you can differentiate within an inequality
This is the original question
Ohhhh
I want to find when its increasing, so I differentiate and set it > 0 right?
reduee it to a set intersection
^^
wym sry?
{f is concave down} n {f is increasing}
Both sets you know how to find
Yeye I think I can solve it, I was just wondering about this ^^ Like does dividing both sides by (x-2) count as dividing by a minus? to switch the sign direction
Like is it (6x) > 0 and (x - 2) > 0
or (6x) < 0 and (x - 2) > 0
If x is greater than 2, will dividing by x-2 be like dividing by a plus or a minus?
the only correct and general thing you can say about handling inequalities is to be extra careful
I feel like its this one
But I thought I was supposed to get an x> and x<
Not x> and x>
plus
Yeah, so you have to make two cases: when x>2, and x<2. Dividing by x-2 will be like dividing by a plus and a minus respectively
Then i hope you can see how to solve your inequality
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I don't want the answer, just clarifications about what is asked. Question says to replace the ? by an explicit number so that the equalities are true for any x with denominator being different than 0.
Does the ? mean like a y constant or something ? Like, it should be only one number, it can't be different numbers ?
yes you're looking for 3 constants to replace the ?
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im not really sure how do to this
i know how to determine if something is a subspace of another vector space
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Hello, how does one come up with the formula for 1^2+2^2+...+n^2?
i saw a suggestion that was like
well, you might guess that, because the sum of the first n numbers is quadratic in n
that the sum of the first n squares may be cubic
so you guess it has some form like $an^3+bn^2+cn+d$
jan Niku
yeah now its simple
and then solve for these coefficients
you have no reason to believe this will be true
but the fact that it has to be a polynomial
its just a guess
doesnt really click with me
do you know any calculus
i mean just the power rule provides some loose motivation for why you might expect this relationship
caluculus
jan Niku
the area under this function $x$ from $x=0$ to $x=n$, say, is $\frac{n^2}{2}$
jan Niku
which we get by using FTC, power rule
maybe you can see where I'm going?
you can kind of think of the sum of the first n numbers as something like this
were adding up areas
theres a rectangle 1 wide, 1 high for n=1
then a rectangle 1 wide, 2 high for n=2
ooh
all of these sit under the function f(x) = x
yes
so our area of rectangles is gonna be less than this formula
and it is
sum of rectangles is $\frac{n(n-1)}{2}$
jan Niku
instead of $\frac{n(n)}{2}$
jan Niku
so, you might reason that if we instead took $f(x) = x^2 \dots$
jan Niku
hopefully that makes sense
yes it does
why
yeah
the sum 1+2+... gives us the area under the green rectangles
so we actually expect that formula to give us a bigger answer
and it does
i got the formula wrong
its actually $S_n = \frac{n(n+1)}{2}$ instead of $\frac{n(n)}{2}$ by calculus
jan Niku
heres the picture for n^2 vs x^2
you know the formula for area under the black curve, by just integrating
yes similarly
sure
its a system of 4 equations
but if you know any intro linear algebra
or feel comfortable solving systems
youll make quick work of it
yeah its just computation
yea
you need 4 data points, but thats easy, you can just calculate them
yadda yadda
derive the formula, simplify
youll be there

thank you!
np
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Hi
This is my question
Work so far
I need to sketch a possible graph for y = f(x)
I also know that I have to find the antiderivative to do this
you have everything you need really
what do you think its general shape is?
sure i suppose, though you dont need to
Also is part a and b correct so far
Ok forgot the antiderivative part but how can I graph this
your table does not seem right
everything after the first box
Then what should i put in it
explain where you were getting your numbers and results from
Well idk what the intervals are
have you really looked at the graph?
what dont you get though
f'(x) is positive when its above the x axis, negative when below, and 0 when intersecting it
Oh so is it like x < -3, -3 < x < 0, 0 < x < 1 and x > 1
What are the intervals thats all i am asking
x<-1, -1<x<1, x>1
do you mean row?
yes
if you fix the titles, then sure theyre fine
Yes still what would the shape of the graph be
if f'(x) is a quadratic, what must f be
Linear
youre going the wrong way
Cubic
,w graph x^3
you still need to use the info you have though to make it more accurate
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Hello I need help with multiple questions but this is one of them. Idk how to apply log laws to questions
The correct working out is just this but idk how they got x^2/x^2
exponent/radical laws
convert sqrt(x) to exponential form
or x^(3/2) to radical form depending on personal preference
also don't use x for multiplication especially when variable x is present
Okk 👍
where you see stuff like $\sqrt{}$, those are called radicals
ℝαμΩℕωⅤ
How is 3/2 radical
Oh
But why would i do that
Wouldnt that make it harder to solve
it's about the same
3 sqrt x?
This isn’t my working out
This is the right working out but idk how they got that
Especially 2nd line
after converting sqrt(x) to x^(1/2),
you'll have
x^(1/2) * x^(3/2)
on the numerator
can you simplify that?
X^1/2
no
….
Oh
Im so stupid
💀💀💀💀💀
Oh ok
Wait
I have other questions if you have time
I got this one, my brain was just malfunctioning
?
what's your q
It says express the following as logarithm statements with the index as the subject for 4^3/2 = 8
The index is 4^3/2 isn’t it? How do i make that the subject in a log statement?
Nevermind I got it, thank u
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@atomic seal Has your question been resolved?
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Like to solve p(x) /g(x)
!original
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
We find zero of g(x)
show the full thing
If g(x) is x-1
its cut off
!original
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
ok. that's most definitely related
But I'm just asking
That
Like for example g(x) = x-1
It's zero is 1
So if we assume x value as 1
It makes g(x) =0
So I don't get it
What does it mean by g(x) is not equal to 0
Does it mean that g(x) literally can't be 0
Or that whatever polynomial is there it can't be equal to 0
It says g(x) shouldn't be equal to 0
means that g(x) isn't the constant 0



