Choose the correct answer from the given four options : Which of the following is not a quadratic equation?

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(x + 2)2 = 2(x + 3) ⇒ x2 + 4x + 4 = 2x + 6 ⇒ x2 + 4x – 2x + 4 – 6 = 0 ⇒ x2 + 2x – 2 It is a quadratic equation. x2 + 3x = ( – 1) (1 – 3x) ⇒ x2 + 3x = –1 + 3x ⇒ x2 + 1 = 0 it is also quadratic equation. (x + 2) (x – 1) = x2 – 2x – 3 x2 - x + 2x - 2 = x2 - 2x - 3 x2 - x2 + x + 2x - 2 + 3 = 0 ⇒ 3x + 1 = 0 It is not a quadratic equation. x3 – x2 + 2x + 1 = (x + 1)3 = x3 + 3x2 + 3x + 1 x3 - x2 + 2x + 1 3x2 + x2 - 2x - 1 + 3x + 1 = 0 ⇒ 4x2 + x = 0 It is a quadratic equation.

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