Question

5. cos A cos (B - A) - sin A sin (B - A) =
(a) sin A
(b) cos A
(C) sin B
(d) cos B​

Answer 1

Answer:

(d) cos B

Step-by-step explanation:

Let (B-A) = X

Therefore,

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

= cos A cos X - sin A sin X

= cos (A+X), [as cos (A+B) = cos A cos B - sin A sin B]

= cos (A+B-A)

= cos B

Hope it helps!!!!