f (x,y) = ax^2+2bxy+cy^2 (a,b,c not all zero!) the contours of the function form either a family of ellipses or hyperbola centered at the origin. To determine which how to find the maximum and minimum values of f subject to x^2+y^2=1. Then if both values have the same sign (i.e. max and min) the family consists of ellipses or hyperbola??why??