Question

What does `3cos(arcsin(5))-6sec(arctan(5))` equal?

Answer 1

arc sin 5 is invalid arc sin. I have given this answer many a time to such questions on values of expressions carrying invalid arc sin and invalid arc cos.

Explanation:

Let a = arc sin 5. Then sin a = 5 > 1. So, arc sin 5 is invalid.

For any a, `|sin a|<=1`. Indeed this applies to arc cos also.