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.