Question

What is cos-1 (-1/sqrt2)?

Answer 1

Common, you can really look that up in any formula book or at wikipedia. Just look for special values of trigonometric functions.

Answer 2

Oh you're helpful.

Answer 3

It might look more familiar if you rationalize.

Answer 4

I suppose this is meant ironically. But I will forgive your misguidedness.
Asking others for a solution to a specific problem will not bring you far. There will not always be someone competent there to help you.
The basics in every science and especially math is looking things up in the literature, furthermore as these topics are so common.

Answer 5

Isn't this site meant for people who are having trouble to get help from other people?

Answer 6

Yes, only not for letting others solve their assignments, but being taught how to do it. And I told you, this can be looked up quite easily.

Answer 7

Yes, you told me to "look it up." That's not very helpful. It's more rude than anything. If I knew what it was, I wouldn't have posted this.

Answer 8

Calm down and be rational. See what i did there?

Answer 9

cos-1(A) = B is equivalent to saying
A = cos(B)

Answer 10

so if cos-1(1/sqrt(2)) = B means
1/sqrt(2) = cos(B)

Does that help at all ?