Question

find y' and y'' y=cos^2x
I have y' as 2(cosx)(-sinx)=-sin2x
for y'' all I can come up with is -cos2x-sin2, is that right?

Answer 1

y' is correct
for y'' you failed to use the chain rule
let u=2x-> u'=?
\[(-\sin(u))'=-\cos(u)\cdot u'\]

Answer 2

ah, got it, I used the product rule instead of the chain rule

Answer 3

thank you

Answer 4

welcome