Using the addition or subtraction formulas for sine or cosine ... sinasinb = (cos (a-b) - cos (a+b)) / 2

The answer w'll be obtained using formulas

cos (a+b) = cosacosb - sinasinb

cos (a-b) = cosacosb + sinasinb

Step-by-step explanation:

Using the trigonometric formula of addition and subtraction of cosine

cos (a+b) = cosacosb - sinasinb

cos (a-b) = cosacosb + sinasinb

w'll get the desired answer.

To be solve

L. H. S = R. H. S

sinasinb = (cos (a-b) - cos (a+b) / 2

as we know that cos (a+b) = cosacosb - sinasinb

sinasinb = (cos (a-b) - (cosacosb - sinasinb)) / 2

as we know that cos (a-b) = cosacosb + sinasinb

sinasinb = ((cosacosb + sinasinb) - (cosacosb - sinasinb)) / 2

sinasinb = (cosacosb + sinasinb - cosacosb + sinasinb) / 2

sinasinb = (2sinasinb) / 2

sinasinb = sinasinb

hence L. H. S = R. H. S