I hope that from the graph, it is obvious that if the y-coordinates are to be the same, the x-coordinates now needs to be halved, and thus the horizontal stretching has scale factor [math]\frac{1}{2}.[/math]
Horizontal Stretching
If a function [math]f[/math] has its input [math]x[/math] multiplied by a constant [math]q[/math] , then the graph of [math]f[/math]f is stretched by a scale factor of [math]\frac{1}{q}[/math] horizontally/parallel to the x-axis. [br][br][math]g\left(x\right)=f\left(qx\right)[/math]