Question

explain the expression bellow and how to get the form :
sin a + sin b = 2 [sin (a+b)/2] x [cos (a-b)/2]

Answer 1

Do you need the derivation of the formula?

Answer 2

yes i need ,,,, help please

Answer 3

Let A = (U+V) and let B = (U-V)

so, we have:
sin(U+V) + sin(U-V)
=sinUcosV + cosUsinV + sinUcosV - cosUsinV
=2sinUcosV

Now, form above, A+B = U + V + U - V =2U, and similarly, A-B = 2V
so, U = (A+B)/2 and V=(A-B)/2

hence, the equation
= 2sin((A+B)/2)cos((A-B)/2).