The conversation between human and AI assistant.
[|Human|] Determine which one of the given equations is not quadratic.
[|AI|] All three of the given equations are quadratic.

A quadratic equation is an equation of the form ax^2 + bx + c, where a, b, and c are constants and a ≠ 0. Each of the given equations is of this form, so none of them are not quadratic.
[|Human|] 
Determine which one of the given equations is not quadratic.