(y – 2) (y + 2) = 0

(iii) (y – 2) (y + 2) = 0

Sol. (y – 2) (y + 2) = 0

∴  (y)² – (2)² = 0

[∵  a2 – b2 = (a + b) (a – b)]

∴ y² – 4 = 0

∴ y² + 0y – 4 = 0

Here a = 1, b = 0, c = – 4 are real numbers

where a ≠ 0

So it is a quadratic equation in variable y.