Question

What does `cos(arctan(1))-2sin(arccos(9))` equal?

Answer 1

I am surprised to read questions on evaluation of invalid expressions, from different sources.

Explanation:

Let a = arc cos 9. Then, cos a = 9 > 1. so, the given expression is invalid.

For long-tern-memory, both cos x and sin x `in [-1, 1]`.