Question

Jake throws a stone off a bridge into the river. The stones height in meters above the water is based on the time in seconds after jake threw the stone. The quadratic equation y=-5^2+10x+15 represents the scenario

Answer 1

Answer:

The stone will hit the water after 3 seconds

Step-by-step explanation:

Given

$y = -5x^2 + 10x +15$

Required

At what time will the stone enter the water

When the stone enters the water;

$y = 0$

So, we have:

$-5x^2 + 10x +15 = 0$

Divide through by -5

$x^2 -2x -3 = 0$

Expand

$x^2 +x -3x -3 = 0$

Factorize

$x(x +1) -3(x +1) = 0$

Factor out x + 1

$(x -3) (x +1) = 0$

Solve for x

$x - 3 = 0\ or\ x + 1 = 0$

$x = 3\ or\ x = -1$

x (time) cannot be negative.

So:

$x = 3$