Reposted: Maths  Trig
posted by xX_Supaman_Xx .
I've been told that
sin(c+h)=sin(c)xcos(h)+cos(c)xsin(h)
but how?
please explain

Here you will find a proof of that trigonometric identity:
http://library.thinkquest.org/C0110248/trigonometry/formsine.htm 
Here is another approach to the proof
http://www.themathpage.com/aTrig/sumproof.htm
(there seems to be a 'spacing' problem in the html code in the first few lines, but I am sure you know what the equation should read )