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jmc

algebra senior

Problem

A portion of the graph of a quadratic function is shown below.

Let and . If is the number of points where the graphs of and intersect, and is the number of points where the graphs of and intersect, then what is ?

problem
Solution
Note that the graphs of and are the reflections of the graph of across the -axis and the -axis, respectively. Thus, the original graph intersects these two graphs at its -intercepts and -intercepts, respectively. This is shown in the following picture: Since the original graph has 2 -intercepts and 1 -intercept, we have and . Since the original function is not invertible, it intersect its reflection across the -axis elsewhere than at a -intercept, but the graph clearly shows that it does not, so and .
Final answer
21