A quadratic function is of the form:

That is, a function of degree 2.
- In this case, the function

It is a function of degree 2, so it is a quadratic function.
- For the function

We see that it does not have a term of degree 2, therefore it is not a quadratic function.
- And for the function

It is a function of degree 3, therefore, it is not a quadratic function.
Answer:
