Question

Out of the following equations which one is not a quadratic equation?

Options

• x² + 4x = 11 + x²

• x² = 4x

• 5x² = 90

• 2x – x² = x² + 5

Answer 1

x² + 4x = 11 + x²

Explanation:

1. x² + 4x = 11 + x²
   `\implies` 4x = 11
   Thus, x² + 4x = 11 + x² is not a quadratic equation.
2. x² = 4x can be written as x² – 4x + 0 = 0
   So, x² – 4x is a quadratic equation.
3. 5x² = 90 can be written as 5x² – 90 + 0 = 0
   So, 5x² – 90 + 0 is a quadratic equation.
4. 2x – x² = x² + 5 can be written as 2x² – 2x + 5 = 0.
   So, it also forms a quadratic equation.

Hence, the correct answer is x² + 4x = 11 + x².