## Precalculus (10th Edition)

$f(3x) = -18x^2+4$
RECALL: $f(a)$ represents the value of the function $f$ when $x=a$. Substitute $3x$ into $x$ in the function $f$ to obtain: $f(3x) = 4-2(3x)^2 \\f(3x) = 4-2(9x^2) \\f(3x) = 4-18x^2 \\f(3x) = -18x^2+4$