Hi Guys !
Here is yet another trigo identity which i simply can't figure it out
please help thanks !
sinA + sinB + sin(A+B) = 4sin{ (A+B)/2 }cos(A/2)cos(B/2)
1. Rewrite $\displaystyle \sin\alpha+\sin\beta$ using the sum-to-product rule.
2. Rewrite $\displaystyle \sin(\alpha+\beta)$ as $\displaystyle \sin(2(\alpha+\beta)/2)$ and further using the formula for double angle.
3. Factor out $\displaystyle 2\sin((\alpha+\beta)/2)$ in the left-hand side.
4. To the remaining sum of cosines in the left-hand side, apply the sum-to-product rule.