8. Show that f(x,y) =
is continuous at every point except the origin. (10%)
7. Water runs into a conical tank at the rate of 9 ft³/min. The tank stands point down and has a height of 10 ft and a base radius of 5 ft. How fast is the water level rising when the water is 6 ft deep? (see the figure below) (10%)
the conical tank in problem 7.
20. 已知 t 為實數,若線性方程組 ,有無限多組解,則 t =?
(A) -2
(B) -1
(C) 0
(D) 1
19. 矩陣 A = 的秩(rank)為何?
(A) 1
(B) 2
(C) 3
(D) 不存在
18. 下列各矩陣中,何者無反矩陣(inverse matrix) ?
(A) (B)
(C)
(D)