4. Set f(x, y) = x² + 2y². Which of the following must be true? (A) f(x, y) is concave upward on the line $y = -x (B) the relative minimum of f(x, y) subject to the constraint x + y = 1 is (C) the absolute minimum of f(x, y) on its domain does not exist (D) the minimum rate of change of f(x, y) at the point P(1, -1) is 

3. Which of the following must be true? (A) The series converges for all p≠0$ (B) The series converges absolutely (C) The series converges (D) The series   diverges

2. Which of the following must be true? (A) (B) (C) (D)