Question

Find dy/dx when:

x= sin2A y= cos4A

Answer 1

Parametric equation?

Answer 2

Yes it is, sorry, I forgot to mention that!

Answer 3

y=cos4A
dy=-4sin(4A) dA

dy/dA = -4sin(4A)

x=sin2A
dx=2cos(2A) dA

dx/dA = 2cos(2A)

Use chain rule,
dy/dA = (dy/dx)(dx/dA)

dy/dx= (dy/dA)/(dx/dA)

dy/dx = -2sin(4A)/cos(2A)

Answer 4

dunno if it works

Answer 5

Thank you all so much! :) I have a test later on and trig is a weak point ;) thanks for clearing that up though, much appreciated.

Answer 6

@Callisto, the answer I have with the worksheet is -4sin2A.. thanks though, i've got it now :)

Answer 7

y = cos4a --> y' = -4sin4a = -8sin2acos2a
x = sin2a ---> x' = 2cos2a
-> y'/x' = -4sin2a