Thread: proof

i need to prove sinx-siny= 2 sin( (x - y)/2 ) cos( (x + y)/2 )

here is a simple say.

for some x and y.

after applying the sine addition and subtraction formulas,

, you will end up with

now note that we want this in terms of a and b so we have

and so using this we have

Hello, lexmex1546!

This is a rehash of putnam120's solution . . . with baby steps.

Prove: .

We have these two formulas:

. .
. .

Subtract (2) from (1): .

Let: .

Then (3) becomes: .