Question

The quadratic function d = -2x^2+ 10 models a skateboarders distance,

in feet, from the bottom of a hill, x seconds after the skateboarder starts moving down the hill.
After how many seconds, is the skateboarder 1 ft from the bottom of the hill?

Answer 1

2.1 seconds

Explanation:

Note we are told that d = -2x² + 10, where d is distance (in feet) and x is time (in seconds).

After how many seconds is the skateboarder 1 ft from the bottom of the hill? => What is x when d=1?

To do this, sub 1 in for d and solve for x:

d = -2x² + 10

1 = -2x² + 10

-9 = -2x²

4.5 = x²

x =
`√(4.5)` ≈ 2.12132