Sum and Difference Identities

Just a reminder:

Deriving sin(x+y)



For sin(x-y) switch the + to a - 

sin(x-y) = sinxcosy - cosxsiny

For cosine identities of sum and differences the operations are opposite

cos(x+y) = cosxcosy - sinxsiny

cos(x-y) = cosxcosy + sinxsiny

Deriving Tangent