Question

Is it right to say cos(60° + 30°) = cos 60°cos 30° − sin 60°sin30°.

Answer 1

yes, we can say because cos90 = 0 and cos60cod 30 and sin60sin30 will canel out to get 0. so we will get L.H.S= R.H.S

Answer 2

Answer:

We know that,

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

= $\frac{1}{2}$ x $\frac{\sqrt{3} }{2}$ - $\frac{\sqrt{3} }{2}$ x $\frac{1}{2}$

= $\frac{\sqrt{3} }{2} - \frac{\sqrt{3} }{2}$ = 0

⇒ cos (60° + 30°)

We know that,

= cos (A + B) = cos (60 + 30)

= cos 90°

⇒ 0

Hence, Yes it is right to say that

cos(60° + 30°) = cos 60°cos 30° − sin 60° sin 30°

⇒ LHS = RHS