Just use the product rule as with regular diff except treat x as a constant.
oh right, well i got the same, only with the 1st term multiplied by y :s either way, its still a bit compicated. im actually doin a greens theorem problem
integral {(xy - 4x^4y - y(x^2+y^2)^1/2 + 1/2 y^2sinx)dx + (4xy^4 + 8/3x^3y^2 + x(x^2+y^2)^1/2 - ycosx) dy}
its not cancelling like it ought to when i try it