Question

What does `4sin(arccos(2))-cos(arctan(4))` equal?

Answer 1

arc cos 2 is invalid. This is an angle whose cosine is 2. But numerically a cosine cannot exceed 1.

Explanation:

If `a=arc cos 2. cos a = 2 > 1, |cos x| <=1`. So, arc cos 2 is unreal.