The quadratic function above models the height above the ground h , in feet, of a projectile x seconds after

Question

The quadratic function above models the height above the ground h , in feet, of a projectile x seconds after it had been launched vertically. If is graphed in the xy -plane, which of the following represents the real-life meaning of the positive x -intercept of the graph?

Accepted Answer

Choice D is correct. The positive x -intercept of the graph of is a point for which . Since models the height above the ground, in feet, of the projectile, a y -value of 0 must correspond to the height of the projectile when it is 0 feet above ground or, in other words, when the projectile is on the ground. Since x represents the time since the projectile was launched, it follows that the positive x -intercept, , represents the time at which the projectile hits the ground. Choice A is incorrect and may result from misidentifying the y -intercept as a positive x -intercept. Choice B is incorrect and may result from misidentifying the y -value of the vertex of the graph of the function as an x -intercept. Choice C is incorrect and may result from misidentifying the x -value of the vertex of the graph of the function as an x -intercept.

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