Question

sinx=1/2 siny=1/3 ,sin(x+y)(sinx-y)=?

Answer 1

sin(x+y)sin(x-y)=[sinxcosy+cosxsiny][sinxcosy-cosxsiny]

=(sinxcosy)^2-(cosxsiny)^2

=(sinx)^2[1-(siny)^2]-[1-(sinx)^2](siny)^2

=1/4*(1-1/9)-(1-1/4)*1/9

=5/36