6) [15 points] Consider the function f(x,y) = guy 2 . x\" + y . . . 6f 6f . a) Calculate the partial derivatives T and 6 at the pomt (x, y) = (2,1) . ox y 31y x2 +y2 b) Find the directional derivative of f (x, y) 2 at the point (2,1) in the direction of the vector v=(3,4). 3%? x+y c) Find an equation for the tangent plane to the graph of the function f(x, y) = (Ly): (2,1)- at the point where