To Prove:

Formula Used:

1)

2)

Proof:

LHS … (1)

… (2)

Substituting (2) in (1), we get

LHS … (3)

Let

Therefore … (4)

From the figure,

… (5)

From (4) and (5),

… (6)

Substituting (6) in (3), we get

LHS

= tan^-1 1

= RHS

Therefore, LHS = RHS

Hence proved.