Question

Find the exact value of the expression:
cos^-1 (cos(-3π/5)) Explain please!

Answer 1

cos and cos inverse cancel

Answer 2

So the answer is -3π/5?

Answer 3

yup

Answer 4

It said that the answer is 3π/5, without it being negative o:

Answer 5

interesting

Answer 6

How's that possible?

Answer 7

That's because cos(-x) = cos(x).
You can check by doing cos(0-x) :)

Answer 8

Oh, okay! Thank you guys

Answer 9

\[\cos (0-x) = \cos 0*\cos x + \sin 0*\sin x\]Thus,\[\cos (0 - x) = 1*\cos x + 0*\sin x\]So\[\cos(0 - x)=\cos x \leftarrow \rightarrow \cos(-x) = \cos(x)\]

Answer 10

So does it work like that for sin, tan, cot, csc, and sec?

Answer 11

Not really. You gotta check the other ones by using trig identities.
Here's a list: http://en.wikipedia.org/wiki/List_of_trigonometric_identities

Answer 12

Alrighty, thanks!