Answer
$f(x)=-2(3+x)^2+2x^2$ is a "Linear Function"
Work Step by Step
$f(x)=-2(3+x)^2+2x^2$ is a linear function as the highest degree/order term is $x$
After simplifying the above expression, we get $f(x)=-12x-18$
Here$-12x$ is the linear term and $-18$ is the constant term