Answer: No, it is not a linear function. It is a Quadratic function.
Explanation:
 Given the following function:
 

 You need to apply Distributive property:
 

 

 
 You can observe that the highest exponent of the function is "2", therefore, it is not a Linear function, but a Quadratic function in the form:
 

 Where a, b, and c are numbers (
 )
)