If A, B and C are the interior angles of any triangle ABC then prove that

Given: A, B and C are the interior angles of triangle.

⇒ A + B + C = 180˚

⇒ B + C = 180˚ – A

Dividing by 2 both sides of above equation,

⇒ = 90˚ –

⇒ Taking Tangent both sides,

⇒ tan () = tan (90˚ – )

⇒ tan () = cot () (tan (90˚ – θ) = cot θ)

Hence, proved.