SAT Mathematics Practice Test 7

The graph of a quadratic function in the xy-plane is a parabola. The axis of symmetry of t he parabola passes through the vertex of the parabola. Therefore, the vertex of the parabola and the midpoint of the segment between the two x-intercepts of the graph have the same x-coordinate. Since f(–3) = f(–1) = 0, the x-coordinate of the vertex is $\frac{\left(-3\right)+\left(-1\right)}{2}=-2$. Of the shown intervals, only the interval in choice B contains –2.