Question

Given A = (3, 1) and B = (0, y - 1). Find y if AB = 5.

Answer 1

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