Question

The function f(x) = −x^2 − 5x + 50 shows the relationship between the vertical distance of a diver from a pool's surface f(x), in feet, and the horizontal distance x, in feet, of a diver from the diving board. What is a zero of f(x), and what does it represent?
x = 5; the diver jumps in the pool at 5 feet per second
x = 10; the diver jumps in the pool at 10 feet per second
x = 10; the diver hits the water 10 feet horizontally from the board
x = 5; the diver hits the water 5 feet away horizontally from the board

Answer 1

Set the function to equal zero:

$-x^2 - 5x + 50 = 0$

To find the zeros, or solutions, to this problem, we will use the quadratic formula:

$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$

Plug the values into the equation:

$a = -1, b = -5, c = 50$

$x=\frac{5\pm\sqrt{-5^2-4(-1)(50)}}{2(-1)}$

$x=\frac{5\pm\sqrt{25+200}}{-2}$

$x=\frac{5\pm15}{-2}$

Solve for both plus and minus:

$\frac{5 + 15}{-2} = \frac{20}{-2} = -10$

$\frac{5 - 15}{-2} = \frac{-10}{-2} = 5$

$x = -10, x = 5$

The question cannot use a negative value for x, as the diver cannot dive a negative distance from the board.

The answer is 'x = 5; the diver hits the water 5 feet away horizontally from the board', because x represents the horizontal distance away from the board.