text: implicit differentiation? computer the slopeof y^2 + 2xy + 4 = 0 at (-2,2) 1) y^2+2xy+4=0  2) 2y(dy/dx)+2y+2x(dy/dx)=0  3) (dy/dx)(2y+2x)=(-2y)  4) dy/dx=(-2y)/(2y+2x)  5) when you plug in (-2,2) :   dy/dx = -4/0  6) thus slope is equal to infinity or does not exist