Question

what does the transformation $f(x) \mapsto f(2x)$ do to the graph of $f(x)$?
shrinks it vertically
shrinks it horizontally
stretches it horizontally
stretches it vertically

Explanation:

For function transformations, when replacing $x$ with $kx$ where $k>1$, the graph of $f(x)$ undergoes a horizontal compression by a factor of $\frac{1}{k}$. Here $k=2$, so the graph shrinks horizontally.

Answer:

shrinks it horizontally