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FP2

the.cookie.monster

Anyone do FP2?

Attachment not found

What I attempted so far:
Differentated with respect to t to get dy/dt=-2x^-3(dx/dt)
Then I differentiated again to get d2y/dt2=6x^-4(dx/dt) -2x^-3(d2x/dt2)
Then rearranged the subjects so I could sub back into the original equation~got stuck along the way though and I'm not anywhere close to the proof :O
We got given the CD to help with revision over Easter but I can't seem to work out how to open solution bank on my laptop :/

Reply 1

Gray Wolf

I would love to help but there is a problem with the link.

Reply 2

the.cookie.monster

Original post by Gray Wolf

I would love to help but there is a problem with the link.

Oh did it not attach :redface:

Reply 3

Indeterminate

Original post by the.cookie.monster

Oh did it not attach :redface:

You've done the tricky bit right. Now it comes down to this: how solid is your algebra?

(edited 11 years ago)

Reply 4

the.cookie.monster

Original post by Indeterminate

You've done the tricky bit right. Now it comes down to this: how solid is your algebra?

Okay, well when I rearranged I got:
dx/dt=-0.5x^3(dy/dt)
d2x/dt2=-0.5x^3(d2y/dt2)+3x^-1(dx/dt)
Subbing in I get:
-x^4(d2y/dt2)+6(dx/dt)-6(-0.5x^3(dy/dt))^2=x^2-3x^4
I don't see how I would be able to get rid of (dy/dt)^2

Reply 5

Indeterminate

Original post by the.cookie.monster

\frac{d^2 y}{dt^2} = 6x^{-4}(-0.5x^3 \frac{dy}{dt}) -2x^{-3} \frac{d^2 x}{dt^2}

Reply 6

the.cookie.monster

Original post by Indeterminate

\frac{d^2 y}{dt^2} = 6x^{-4}(-0.5x^3 \frac{dy}{dt}) -2x^{-3} \frac{d^2 x}{dt^2}

I've realised what I did wrong now-I differentiated incorrectly d2y/dt2
I was supposed to get 6x^-4(dx/dt)^2 -2x^-3(d2x/dt2)
:redface:

but thanks anyway :smile:

Reply 7

Indeterminate

Original post by the.cookie.monster

I've realised what I did wrong now-I differentiated incorrectly d2y/dt2
I was supposed to get 6x^-4(dx/dt)^2 -2x^-3(d2x/dt2)
:redface:

but thanks anyway :smile:

Was about to say that as I was doing the Q from scratch. You were too quick :smile:

By the way, my last post refers to the fact that

d2x/dt2=-0.5x^3(d2y/dt2)+3x^-1(dx/dt)

was an incorrect deduction from the wrong differentiation :smile:

(edited 11 years ago)