Question

plzzz answer sooon... prove this plzz plzzz plzzzzzz​

Answer 1

Given A+B+C = 180

C = 180 -( A+B)

cos C = cos 180 - (A +B) = - cos (A+B)

now, Sin^2A + 1 - Cos^2B + Sin^2C

1 -(Cos^2B - Sin^2A) + Sin ^2C

1 - Cos (A+B) Cos (A - B) + 1- Cos^2C

2 + CosC [Cos(A -B) + Cos ( A + B)]

2 + 2 Cos A CosB CosC

Hence L.H.S = R.H.S