The function f(x,y)= -x^4-256x+y^3-75y+9 has two critical points. Enter them in order of increasing y-coordinate and classify each as a local minimum, local maximum, or saddle point. First point? Second point? Solution df/dx = 4x^3 - 256 = 0 => x = -4 df/dy = 3y^2 - 75 => y = +5,-5 Thus (-4,-5) is local max (-4,5) is saddle point..