Question

______cos b= 1/2[sin(a+b)+sin(a-b)]. A. cos a B. sin a C. cos b D. sin b

Answer 1

sin(a+b) = sinacosb + cosasinb

sin(a-b) = sinacosb -  cosasinb

adding we get  sin(a+b) + sin(a-b) = 2sinaccosb

so sinacosb = 1/2sin(a+b) + sin(a-b)

Answer: Sin a