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Advanced Math / Nonlinear equations in one variable and systems of equations in two variables Difficulty: Hard

In the xy-plane, the graph of y equals 3 x squared minus 14 x intersects the graph of y equals x at the points with coordinates zero comma zero and a, comma a. What is the value of a ?

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Explanation

The correct answer is 5. The intersection points of the graphs of y equals, 3 x squared, minus 14 x and y equals x can be found by solving the system consisting of these two equations. To solve the system, substitute x for y in the first equation. This gives x equals, 3 x squared, minus 14 x. Subtracting x from both sides of the equation gives 0 equals, 3 x squared, minus 15 x. Factoring 3 x out of each term on the left-hand side of the equation gives 0 equals, 3 x times, open parenthesis, x minus 5, close parenthesis. Therefore, the possible values for x are 0 and 5. Since y equals x, the two intersection points are the points with coordinates 0 comma 0 and 5 comma 5. Therefore, a, equals 5.