Question

The quadratic function y = -x2 + 10x - 8 models the height of a trestle on a bridge. The x-axis represents ground level.
To find where the section of the bridge meets ground level, solve 0 = -x2 + 10x - 8.
Where does this section of the bridge meet ground level?

Answer 1

Answer: 0.876, 9.123

Step-by-step explanation:

The function is $y=-x^2+10-8$

It meets the ground level when $y$ is 0

$\Rightarrow -x^2+10x-8=0\\\Rightarrow x^2-10x+8=0\\\\\Rightarrow x=\dfrac{10\pm \sqrt{(-10)^2-4(1)(8)}}{2}\\\\\Rightarrow x=\dfrac{10\pm \sqrt{68}}{2}\\\\\Rightarrow x=5\pm \sqrt{17}\\\Rightarrow x=0.876,\ 9.123$

Thus, it touches the ground at two points given above