i have gone ahead and estimated the following equation where y and x are the output and explanatory variables respectively.

Y$=$A $+$ B$*$X$1+$ C$*$X$1^2+$ D$*$X$1*$X$2+$ E$*$X$^2$

I am being challenged by the fact that it is NOT a linear regression model as it involves higher powers of X$1$ and X$2$ as explanatory

variables. What should be my answer?