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Question
Given A = (3, 1) and B = (0, y - 1). Find y if AB = 5.
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Solution
AB = 5
AB2 = 25
(0 - 3)2 + (y - 1 - 1)2 = 25
9 + y2 + 4 - 4y = 25
y2 - 4y - 12 = 0
y2 - 6y + 2y - 12 = 0
y(y - 6) + 2(y - 6) = 0
(y - 6) (y + 2) = 0
y = 6, -2
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