Chapter 15 - Section 15.1 - Functions of Several Variables from the Numerical, Algebraic, and Graphical Viewpoints - Exercises - Page 1094: 11

Neither linear nor interaction function.

$L(x,y) = 3x -2y +6xy -4y^2$ Has y to the power of 2, therefore it is not a linear function. However, the term of $+6xy$ has the product of two variables in it but as these terms are both in the function, it is neither a linear nor an interaction function.