1a.Find the equation of the tangent plane to the surface √ x +
√y + √ z = 4 at P(1, 1, 4).
1b.Let f be a function of x and y such that fx = 3x − 5y and fy
= 2y − 5x, which of the following is always TRUE?
a. (0, 0) is not a critical point of f.
b. f has a local minimum at (0, 0)
c. f has a local maximum at (0, 0)...