65.
(4,−1)(4,−1)
(0, 7)
(6, 9)
67.
x=9, y=6x=9, y=6
71. A=(−a, 0), C=(0,3–√a), D=(0,−3–√a)A=(−a, 0), C=(0,3a), D=(0,−3a)