# 2nd derrivative of y=coskt

• June 7th 2009, 11:11 AM
johntuan
2nd derrivative of y=coskt
Am i doing this right?

y' = -sinkt
y'' = -coskt

??

thanks.
• June 7th 2009, 11:19 AM
Chris L T521
Quote:

Originally Posted by johntuan
Am i doing this right?

y' = -sinkt
y'' = -coskt

??

thanks.

Close...you forgot to apply the chain rule!!

Do these again, and then check the spoiler to see if you're right.

Spoiler:

$y^{\prime}=-k\sin kt$

$y^{\prime\prime}=-k^2\cos kt$
• June 7th 2009, 11:21 AM
johntuan
ahhh...I can't believe I forgot to do such a function..(Headbang)