How do I calculate the following?

Question

tan−1(tan(8)) − tan−1(tan(4))

Answer 1

Recall that the principal values of arctan are -π/2 < x < π/2

tan^-1(tan(8)) = tan^-1(-6.79) = -1.42
tan^-1(tan(4)) = tan^-1(1.157) = 0.858