Find the exact value of sin(140°)cos(20°) – cos(140°)sin(20°)

Given :

An expression sin(140°)cos(20°) – cos(140°)sin(20°) .

To Find :

The value of given expression .

Solution :

We know ,

sin(A - B) = sin A cos B - cos A sin B

By comparing with above formula , we get :

A = 140° and B = 20° .

So , sin(140°)cos(20°) – cos(140°)sin(20°) = sin ( 140°- 20°) = sin 120° .

Now ,

Therefore , the value of expression is .

Hence , this is the required solution .