This is Pissing me off

[Sam Finch]

Can anyone remember the proofs of these Identities?


Sin(a+b) = Cos(a)Sin(b) + Sin(a)Cos(b)
Cos(a+b) = Cos(a)Cos(b) - Sin(a)Sin(b)

[thinktank]

First, I thought of answering this, but then, I saw this page
http://mathforum.org/dr.math/problems/susan5.16.98.html

and they have done a good job..so I am off.

[Lafor]

This question reminds me of how old i am....

sin(A + B)

sin A = cos(pi/2 - A)

sin (A + B) = cos(pi/2 - (A + B))

sin(A + B) = cos ((pi/2 - A) - B)

sin(A + B) = cos(pi/2 - A)cosB + sin(pi/2 - A)sinB

sin(A + B) = sinAcosB + cosAsinB

http://users.erols.com/bram/identities.html