From: Robert Israel on
"M.A.Fajjal" <h2maf(a)> writes:

> How many exact possible solution for
> sin(b)*sin(a+(1/2)*b) = sin(a)*sin((1/2)*a+b)=sin(b+a)*cos((a-b)*(1/2))
> The solutions are not important. But the number of solutions
> How to confirm this number

Infinitely many, of course, since (a=0,b=0) is a solution and the
expressions are all periodic in a and b with period 4 pi.
Or did you want the number of solutions in, say, [0, 4 pi) x [0, 4 pi) ?
I think I counted 24 (graphically).
Robert Israel israel(a)
Department of Mathematics
University of British Columbia Vancouver, BC, Canada