Which of the following is not a quadratic equation?
A quadratic equation is represented by the form,
ax2 + bx + c = 0, a ≠ 0
A. Given, 2(x - 1)2 = 4x2 - 2x + 1
⇒ 2(x2 - 2x + 1) = 4x2 - 2x + 1
∴ 2x2 + 2x – 1 = 0
which is a quadratic equation.
B. Given, 2x - x2 = x2 + 5
∴ 2x2 - 2x + 5 = 0
which is a quadratic equation.
C. Given, 
= 3x2 – 5x
⇒ 
= 3x2 – 5x
∴ 
which is a quadratic equation.
D. Given, (x2 + 2x)2 = x4 + 3 + 4x2
⇒ x4 + 4x3 + 4x2 = x4 + 3 + 4x2
∴ 4x3 – 3 = 0
which is a cubic equation and not a quadratic equation.
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