Which of the following is a quadratic equation?

A quadratic equation is of the form i.e. of degree 2 (a ≠ 0, a, b, c are real numbers)

A. this is not of the form hence it is not quadratic equation.

B.

This is not of the form hence it is not quadratic equation.

C.

This is not of the form hence it is not quadratic equation.

D. using

This is of the form i.e. of degree 2 (a ≠ 0, a, b, c are real numbers)

Hence this is a quadratic equation.