18. Tangent planes Find an equation of the plane tangent to the following surfaces at the given points (two planes and two equations).

18. z = 2+ 2x2 + 2 2 " 1, 3 and (3, -2, 22)30. z = tan xty) 0, 0, 0a. Find the linear approximation to the function f at the given point. b. Use part (a) to estimate the given function value. xty 38. f (x, y, Z) (3, 2, 4); estimate f(2.95, 2.05, 4.02). x- Z