Question

Principal value of tan^-1(- 1) is :

(a) 45°

(b) 135°

(c) – 45°

(d) – 60°

Answer 1

Answer is (c)

∵ tan^-1(- x)= – tan^-1 x

tan^-1 (-1) = – tan^-1(1)

Let tan^-11 = θ

∴ tan θ = 1

⇒ tan θ = tan 45°

∴ θ = 45°

∴ tan^-1(-1) = – 45°