If distance between P and Q, PQ = 10 units, then y = ?
By Squaring on both sides,
y2 + 6y + 73 = 100
y2 + 6y + 73 – 100 = 0
y2 + 6y – 27 = 0
y2 + 9y – 3y – 27 = 0
y (y + 9) – 3(y + 9) = 0
(y + 9) (y – 3) = 0
If y + 9 = 0 then OR y – 3 = 0 then
y = -9 y = 0
∴ y = -9 OR +3.