Question

If b+c=pi prove that 2(1-sinbsinc) = cos(sqr)b+cos(sqr)c?

Answer 1

LIke this? if b + c = pi, then:\[2(1-\sin b+\sin c)=\cos( \sqrt b)+\cos (\sqrt c)\]?

Answer 2

cos square b + cos square c

Answer 3

or squared?

Answer 4

oh, ok.

Answer 5

i fixed one little mistake in the question

Answer 6

man i completely read the statement wrong >.<

Answer 7

oh, ok, i thought i was going crazy.

Answer 8

sorry

Answer 9

Basically, since b + c = pi, we have that sin b = sin c, and we exploit that. I guess I could have done the proof the other way around using that:\[2(1-\sin b \sin c)=(1-\sin b \sin c)+(1-\sin b \sin c)\]\[=(1-\sin ^2b)+(1-\sin ^2c)=\cos^2 b +\cos^2c\]

Answer 10

THANK YOU!