If then A – B is equal to

A very basic idea of Inverse trigonometric function is required to solve the problem.

cos^-1 x + sin^-1 x = π/2 and cot^-1 x + tan^-1 x = π/2

As,

And

∴ A – B =

⇒ A – B =

∴ A – B =

Clearly It matches with option (D)

∴ option(D) is the only correct answer.