#help please

105 messages · Page 1 of 1 (latest)

manic echo
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yep

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you need to differntiation once

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equate it to 0

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solve for x

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then differentiate again and sub in x

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if it's grater than 0 then it is a minimum point

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otherwise it's less than 0 then maximum point

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whats another way to write it

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it's just 9x^-1

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not 1/2

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because if it was -1/2

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then thats sqrt

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yep

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is this meant to be the derivative of y

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you need to watch a youtube video and undersrand this before trying qs probably

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you havent differentiated it correctly

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you need to differentiate the last term

barren ledge
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bro if you don't understand basic differentiation you should probably go learn it yourself

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someone's not gonna explain every step

manic echo
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honestly taking a step back and just going through the whole topic of differentiation and its application will help you

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mhm

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correct

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now solve for 0

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then differentiate this again

manic echo
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into the 2nd derivative

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if it is greater than 0 it is a minimum

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if less than 0 then it's a maximum

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y= 0 and solve for x

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not y sorry

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dy/dx = 0

barren ledge
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do you see that it cancels

regal coral
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multiply through by the denomiantor

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multiply each term by x^2

barren ledge
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they all share a factor of 3

regal coral
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9x^-2 multiplied by x^2 would cancel and give js 9

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oh yeah u could simplify first

barren ledge
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and you can times by x^2 to get it into the form the question wants

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why do you keep saying + -

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just say -

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yes

manic echo
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if you're writing that in exams make sure to put brackets around the - term

barren ledge
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look at the form the question wants it in

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we wanna get this equation into that form

manic echo
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you need to elimate the x^-2 essentially

barren ledge
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yes

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do you see how it resembles a quadratic

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for example we can do z = x^2

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making it z^2 - 2z - 3 = 0

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and we can solve for z and sub back into to get x and show there's 2 stationary points

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yeah

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wait

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what are your values of x

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very close

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we need 2 values of x

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so it's + root 3, - root 3

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because both of them would give 3 when you sub it in

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yeah

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then you can sub in for y

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wait

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that is not the original equation for y

manic echo
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what did you substitute into

barren ledge
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its this

image.png
manic echo
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you need to sub it into the original eq

manic echo
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okay no that's fine

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so now you know that your two stationary points are

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(root3, 0) and (-root3,0)

barren ledge
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no

manic echo
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for what part?

barren ledge
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you need to determine the nature

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of the stationary points

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as well

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bro what

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we are well past 8a

manic echo
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getting the quartic was past a

barren ledge
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solving for the points is 8c

manic echo
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read the q

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what is it asking you to do

barren ledge
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there is no answer it's a show that

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ok you're right that is what it's saying but you don't actually need to sub in root 3 and - root 3 after to show that they satisfy the equation

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all you're doing in this case is algebra to get the equation to that point

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you've already solved for those points and showed that the equation equals 0 for those points

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you showed that when you solved the x-coordinates

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you had 2 different x-coordinates

manic echo
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you need to calculate the 2nd derivative

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d^2y/dx^2

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do you know how to do that

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you need to differentiate the first derivative

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when you differentiated the original eq

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you got dy/dx

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yes?

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now that is your first derivative

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correct

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differentiate your first derivative to get your 2nd derivative

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not quite no

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when you differentiate a constant, it becomes 0

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6 here is a constant

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so when you differentiate

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it becomes 0 not -1

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and when you differentiate the last term

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you need to multiply (-9) by (-2) not just 2

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yep

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you need to sub in your x values of the stationary points into d^2y/dx^2