I presume you mean differentiate with respect to x? To differentiate xy wrt x, we differentiate by parts: differentiate the first operand and multiply by the second, then multiply the first operand by the differential of the second and add the two results: y+xdy/dx. So the complete differential is y+xdy/dx+dy/dx or y+dy/dx(x+1). We cannot take this further because we don't know y in terms of x.