Chapter 4 - Quadratic Functions - 4.2 Graphing Quadratics in Vertex Form - 4.2 Exercises - Page 316: 5

$ |a|\gt1$

The graph of $f(x)= x^2$ will be more narrow for all $ |a|\gt 1$, in other words, for positive constants of $a$ greater that one. See this in action below from the graph. Here, $a= 4$ and $ 8$ for the comparison.