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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, x squared minus 9 intersects line p at the point with coordinates 1 comma a and the point with coordinates 5 comma b, where a and b are constants. What is the slope of line p ?

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Explanation

Choice A is correct. It’s given that the graph of y equals, x squared, minus 9 and line p intersect at the point with coordinates 1 comma a and the point with coordinates 5 comma b. Therefore, the value of y when x equals 1 is the value of a, and the value of y when x equals 5  is the value of b. Substituting 1 for x in the given equation yields y equals, 1 squared minus 9, or y equals negative 8. Similarly, substituting 5 for x in the given equation yields y equals, 5 squared minus 9, or y equals 16. Therefore, the intersection points are the point with coordinates 1 comma negative 8 and the point with coordinates 5 comma 16. The slope of line p is the ratio of the change in y to the change in x between these two points: the fraction with numerator 16 minus negative 8, and denominator 5 minus 1, end fraction, equals the fraction 24 over 4, or 6.

Choices B, C, and D are incorrect and may result from conceptual or calculation errors in determining the values of a, b, or the slope of line p.