Question

Sa se transforme in produs:
cos a - cos b + sin(a + b)

Answer 1

$\it cos a - cos b + sin(a + b) =(cos a - cos b) + sin(a + b)=\\ \\ =-2sin\dfrac{a+b}{2}sin\dfrac{a-b}{2}+2sin\dfrac{a+b}{2}cos\dfrac{a+b}{2} =2sin\dfrac{a+b}{2}\Big(cos\dfrac{a+b}{2}\ -\ sin\dfrac{a-b}{2}\Big)$