Question

Use the 2nd derivative test to find the extremer of f on the interval [0,2PI]
f(x)=2cosx+sin 2x

Answer 1

Ack, I forgot, I don't seem to have a problem with numbers but when it comes to the sin and cos...I am not sure how to derive them. I want to say that 2cosx would end up being something like 2-sinx (x)...but then I feel like there's something wrong w/that scenario.

Answer 2

first derivative:
-2sinx + 2cos 2x
2nd derivative:

-2cosx - 4sin 2x

take it from there