Sum+and+Product

==[|Difficult Trig Problem Practice]==

==[|]==

**Multiplication **
2cos A cos B=cos(A+B) + cos(A-B) 2sin A sin B= -cos(A+B) + cos(A-B) 2sin A cos B =sin(A+B) + sin(A-B) 2cos A sin B=sin(A+B) - sin(A-B)

cos(a) cos(b) = 1/2 [cos(a + b) + cos(a - b)] sin(a) sin(b) = 1/2 [cos(a - b) - cos(a + b)] sin(a) cos(b) = 1/2 [sin(a + b) + sin(a - b)] cos(a) sin(b) + 1/2 [sin(a + b) - sin(a - b)]

**Addition and Subtraction **
cosx +cosy= 2cos1/2(x+y)cos1/2(x-y) cosx -cosy= -2sin1/2(x+y)sin1/2(x-y) sinx +siny= 2sin1/2(x+y)cos1/2(x-y) sinx -siny= 2cos1/2(x+y)sin1/2(x-y)

=Some Videos:=

media type="youtube" key="STWmkwZ-pdE" height="385" width="480" align="left"
Try this link to a clear explanation of Sum and Product formulas: Basic Examples Using Sum-to-Product and Product-to-Sum Formulas