Which of the following is NOT a quadratic equation?

Correct option is A

Concept Used:

A quadratic equation is a polynomial equation of degree 2.

Solution:

Option A:
x(x + 1) + 8 = (x + 2)(x - 2)

x² + x + 8 = x² - 4

x + 8 + 4 = 0

x + 12 = 0 which is not quadratic equation.

Option B:

​$$m(2m + 3) = m^2 + 1$$

2m​² + 3m = m² + 1

2m​² + 3m - m² - 1 = 0

m² + 3m -1 = 0 which is a quadratic.

Option C:
$$(y - 2)^2 + 1 = 2y - 3$$​​
​$$y^2 - 4y + 4 + 1 = 2y - 3$$

$$y^2 - 4y + 4 + 1 - 2y +3 =0$$

y² - 6y + 8 = 0 which is a quadratic.

Option D:

$$(m - 2)^3 = m^3 - 4$$

​$$m^3- 8 -6m^2 +12m -m^3+4=0$$

- 6 m²+ 12m - 4 = 0 which is a quadratic.