Question

I seem to have a mental block with this problem - can someone help please.

If x = sin t and y = cos 2t find dy/dx in terms of x and prove that d^2y / dx^2 + 4 = 0.

Answer 1

i've got as far as finding dy/dx in terms of t.

Answer 2

x = sin t

dx / dt = cos t


y = cos 2t

dy/dt = -2sin2t

Answer 3

dy/dx = -2sin2t / cos t

Answer 4

dy/dx = (dy / dt )/(dx/dt)

Answer 5

ahhh - ok my stupidity i got dy/dt wrong!!!!

Answer 6

thanks yahoo

Answer 7

Welcome...)

Answer 8

my brains in low gear today....