Need help to finish this question,also how do I post in TeXnicCenter?

Find dy/dx and d^2y/dx^2 for x^2y - sin(x^2 - y) = 20

2x. dy/dx - cos(x^2 - y) (2x - dy/dx) = 0

2x. dy/dx = cos(x^2 - y) (2x - dy/dx)

dy/dx = cos(x^2 - y) (2x - dy/dx)/2x

dy/dx . (dx/2x - dy) = cos(x^2 - y)/2x

can't factor out dy/dx

??????????

Thanks.