What is the Exact Value of Cos 135

Answer: By using the formula, Cos(a+b) = cos a cos b – sin a sin b, we will find the value of Cos 135°

Cos 135°= cos(90°+45°)

Let us assume that a = 90° and b = 45°

Cos 135° = (cos 90° cos 45°) – (sin 90° sin 45°)

{As we know that  ,Cos 90°=0

Cos 45°=1/√2

Sin 90°=1

Sin 45°=1/√2}

cos 135°= (0 x 1/√2) – (1 x 1/√2)

cos 135°= –1/√2

The quadrants must be remembered whenever trigonometric computations are performed. The signs are quite important in identifying the proper response.