1. We consider the function f(x, y) = x^4 y+2xy^2 in the direction of which vector do we obtain the maximum value of the derivative of this function at the point (1, 2)?

2-Which of the following equations is that of the plane tangent to the surface z = 2x^2 ? 4y^3 at the point (2, 1, 4)?

A. z =8x -12y +4 B. z = 4x (x -2) -12y2(y - 2) +4 C. 2 = 4 D. z = 8x -12y E. z = 8(x - 2) - 12 (y - 1) +4 F. Cette fonction n'est pas differentiable en ce point et le plan tangent n'existe pas.