Question

I just started calculus. There is a question I can't seem to grasp.
"f(x) = cos2x".
Find f(-pi/4).
I come out with "cos(-pi/2)", but the book says the answer is "0".
Can someone help me out?
Thanks.

Answer 1

Well, can you answer this question:

f(x) = x^2

find f(3)

Answer 2

yeah you just need to evaluate that cos(-pi/2) thingy

Answer 3

Yea, F(3) for F(x) = x^2 is: 9.

Answer 4

Awesome, can you try applying this same concept to the problem you were given? Try your best, I'll help you if you mess up, what's important is you try.

Answer 5

Yes, I came up with cos(-pi/2).
This seems to be in simplest form...

Answer 6

you can simplify that more

Answer 7

cos(-pi/2)=cos(pi/2)
you could use the unit circle