Brilliant! THANKS!

I did something:

polinom:= (a*x^2+b*x*sin(y)+c*sin(y))^2+(a*sin(x)^2+b*x)^3;

t := collect(polinom, [x, sin(y)], recursive);

and i get the wright thing, but when i try to get the coefficient of x*sin^2(y) using:

frontend(coeff, [t, x*sin(y)^2]);

i get this stupid error :(

Error, invalid input: coeff received x*O^2, which is not valid for its 2nd argument, x

Can anyone help me finding the coeff of x*sin^2(y) ?:)

Thanks

Actually i had to find out sin(x+y), i read wrong :)

Thanks!