show that (sin A + cos A) (Sin B + Cos B)= Sin (A +B) + Cos (A-B)

January 28th 2009, 03:56 PM

Mush

Quote:

Originally Posted by dane

show that (sin A + cos A) (Sin B + Cos B)= Sin (A +B) + Cos (A-B)

Expand both of these:

Now factor out sin(A) and cos(A) from the relevant expressions:

Now realise that the inside of the brackets of both sides are identical. Hence the expression in the brackets is a factor of both terms. Take it our as a factor: