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(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.