Question

Prove that how Tan^-1(-1) is 3π/4?

Answer 1

$\tan {}^{ - 1} ( - x) = \pi - \tan {}^{ - 1} (x) \\ \\ \tan {}^{ - 1} ( - 1) = \pi - \tan {}^{ - 1} (1) \\ \\ \tan {}^{ - 1} ( - 1) = \pi - \pi \div 4 \\ \\ \tan {}^{ - 1} ( - 1) = 3\pi \div 4$