The curve $y=f(2x),$ for some function $f,$ is sketched below:

Sketch the curve

One possibility is to work out what $f(x)$ would look like and go from there, but it is possible to be more direct: what could you replace $x$ with in order to make $2x$ into $\frac{x}{2}$ ?

To go from $f(2x)$ to $f\left(\frac{x}{2}\right)$ we replace $x$ with $\frac{x}{4},$ so we need to sketch an enlargement, scale factor $4$, in the $x$ direction.