Question

Cos135 * cos45 +sin135 * sin45 =

Answer 1

Step-by-step explanation:

sin120° can be written as sin(90°+30°)

And… sin(90°+x) =cos x because 90°+x means sin lies in second quadrant and sin is positive in second quadrant.

Therefore…. sin120°=sin(90°+30°)=cos30°

Now cos 135° can be written as cos(90°+45°)

And..cos(90°+x)=-sinx neagative is added before sin here because 90+x means cos lies in second quadrant and cos is negative in second quadrant..

Therefore, cos135°=cos(90°+45°)=-sin45°