Question 309287
{{{sin(x)sin(y)(cot(x)cot(y)-1)= sin(x)sin(y)((cos(x)/sin(x))*(cos(y)/sin(y))-1)}}}


{{{sin(x)sin(y)(cot(x)cot(y)-1)=cos(x)*cos(y)-sin(x)sin(y)}}}


{{{sin(x)sin(y)(cot(x)cot(y)-1)=cos(x+y)}}}