Compute the plane tangent to the graphs at the indicated points using the given functions. (Let z be the dependent variable. If an answer does not exist, enter DNE.) (a) (0, 0)
(i) f(x, y)=xy
(ii) f(x, y)-eX
(iii) f(x, y) = x cos(x) cos(y)
(iv) fx, y) - (x2+ y2) log(x2 + y2)
(b) (0,1)
(i) f(x, y) = xy
(ii) f(x, y) = exy
(iii) f(x, y) = x cos(x) cos(y)
(iv) f(x, y)- (x2 + y2) log(x2 +y2)