#is their a simpler way to do these
129 messages · Page 1 of 1 (latest)
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i know how to do it i just think the way im doing it is too long
How did you start solving it?
eplain in broad terms the details are not that important here
@true hamlet
$\frac{x^2 - 3}{2x^2 + 12x + 18} - \frac{x^2 - 2x + 1}{x^2 - 9} = \frac{-x - 5}{2x + 6}$
TheVinkler
multiply both denomiator a/ b - c/d = a.d - cb / bd
you still there
but it gives me 3rd degreee polinomials
@dense temple
TheVinkler
but it will result in a simple (relatively speaking) polynomial
first you can factorize it in the following way:
$\frac{x^2 - 3}{2(x+3)^2} - \frac{x^2 - 2x + 1}{(x-3)(x+3)} = \frac{-(x + 5)}{2(x+3)}$
and you just go from there
TheVinkler
You need to make a common divisor, which will be $2(x+3)^2(x-3)$
TheVinkler
there most be a more simpler way
where the commun divisors align
its a 1 hour examn with 5 questions like these
there is no way
you need to expand the brackets
then multiply the resut by 2
you are not doing it correctly I beleve
No ofc I am not actually computing that
but the procces looks like this
$(x^2 - 3)(x-3) - 2(x^2 - 2x + 1)(x+3) = -(x+5)(x+3)(x-3)$
TheVinkler
but these is for the denominator only
then you need to multiply the (x^2 -3). (2(x+3)^2(x-3)
once you find the comun denominator you need to multiply it by the upper ones
yes but if the denomentor already has it it cancles out
Yes but why is that
bd= (2(x+3)^2(x-3)
The reason is the following
$\frac{a}{b}-\frac{c}{d}\\
\frac{ad}{bd}-\frac{cb}{bd}\\
\frac{ad-bc}{bd}$
TheVinkler
yeah i get that
ok
thats litteraly what i told you
so now what we are doing is instead of multiplying the entire bd
multiplying by 2(x+3)^2(x-3)
we can take each fraction and multply it by exactly what it needs to become this 2(x+3)^2(x-3)
but im telling you you need to do (x^2 -3)(x-3)(x+3)
(x^2 -3)(x-3)(x+3) = ad
$\frac{(x^2 - 3) \cdot {\color{red}(x-3)}}{2(x+3)^2 \cdot {\color{red}(x-3)}}
- \frac{(x^2 - 2x + 1) \cdot {\color{red}2(x+3)}}{(x-3)(x+3) \cdot {\color{red}2(x+3)}}
= \frac{(-x - 5) \cdot {\color{red}(x+3)(x-3)}}{2(x+3) \cdot {\color{red}(x+3)(x-3)}}$
TheVinkler
This is what I mean
@true hamlet
ok?
after this all the denotators cancel out and it much much more managble
why are you multiplying by (x-3) if the full term is (x-3) (x+3)
In the first 2nd or 3rd fractions?
in the first
exactly,
then you multpily the upper part by the same part missing
and then its more managable right
?
i got it?
if you cancel all of them out you get to the original point
$\frac{(x^2 - 3)(x-3)}{{\color{red} \cancel{2(x+3)^2(x-3)}}}
- \frac{2(x^2 - 2x + 1)(x+3)}{{\color{red} \cancel{2(x+3)^2(x-3)}}}
= \frac{(-x - 5)(x+3)(x-3)}{{\color{red} \cancel{2(x+3)^2(x-3)}}} \
\
&\text{Leaving us with:} \
&(x^2 - 3)(x-3) - 2(x^2 - 2x + 1)(x+3) = (-x - 5)(x+3)(x-3)$
ah okay
TheVinkler
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No, in that case you are right and we will get to the orignal equation
its simpler than i thought
i just forget that you multply by the missing term instead of the whole denominator
thank you
My pleasure
Sure
you do engineering right?
I mean it's fair, but I am a math student currently
Yep
I personally love pen and paper, but a lot of people do prefer the ipads...
I suggest you buy like a 2nd hand from someone else to try it for it bit, see if it works for you
My pleasure, feel free to dm me if you have any other math related question
because im practicing a lot
but they are always new techniques being use
in each excercise
i like math
but its not similar to high school
in anyway
its much harder
well thats it
Glad I could help, your answer for your question should be -21
@true hamlet
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