Hi,
I have an expression which contains terms like cos(3*x)*cos(x) + sin(3*x)*sin(x). In this expression, I replace the prevous terms by using applyrule as:
applyrule([cos(3*x)*cos(x)=1/2*(cos(2*x)+cos(4*x)), sin(3*x)*sin(x)=1/2(cos(2*x)-cos(4*x))],expr);
Is there a way to generalize this so that I may replace all forms of sin(n*x)*sin(m*x) = 1/2(cos((n-m)*x)-cos((n+m)*x))?
Thanks for your help.
