Answer
Option (a)
Work Step by Step
RECALL:
The graph of the function $y=f(ax)$ yields one of the following transformations of the parent function $f(x)$:
(i) horizontal compression when $a\gt 1$; or
(ii) horizontal stretch when $0 \lt a \lt 1$
The given function involves a horizontal compression by a factor of $4$, which means that $a=4$.
Thus, the equation of the function is:
$y=f(4x)$
Therefore, the answer is Option (a).
