Double Angle Formulas of Tan

The sum formula of tangent function is,

tan (A + B) = (tan A + tan B) / (1 – tan A tan B)

When A = B, the above formula becomes,

tan (A + A) = (tan A + tan A) / (1 – tan A tan A) =(2 tan A) / (1 – tan²A)

Thus, the double angle formula of tan function is,

tan 2A = (2 tan A) / (1 – tan²A)