Question

6. Expand cos(A+B+C). Hence prove that B cos A cos B cos C = sin A sin B cos C + sin B sin C cos A + sin C sin A cos B, if A+B+C = + 2 TT​

Answer 1

Answer:

thee answer is given below and its correct, and i know you you are studying at class 11 righ

Step-by-step explanation:

Taking A + B = X and C = Y We get cos (X + Y) = cos X cos Y – sin X sin Y (i.e) cos (A + B + C) = cos (A + B) cos C – sin (A + B) sin C = (cos A cos B – sin A sin B) cos C – [sin A cos B + cos A sin B] sin C cos (A + B + C) = cos A cos B cos C – sin A sin B cos C – sin A cos B sin C – cos A sin B sin C If (A + B + C) = π/2 then cos (A + B + C) = 0 ⇒ cos A cos B cos C – sin A sin B cos C – sin A cos B sin C – cos A sin B sin C = 0 ⇒ cos A cos B cos C = sin A sin B cos C + sin B sin C cos A + sin C sin A cos B