Question

Alain throws a stone off a bridge into a river below. The stone's height (in meters above the water), x seconds after Alain threw it, is modeled by: h(x)=−5x^2+10x+15 How many seconds after being thrown will the stone hit the water?

Answer 1

The correct answer is 3 seconds

Answer 2

Answer:

3 seconds

Step-by-step explanation:

The stone hits the water when h(x)=0

h(x)=0

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

x^2-2x-3=0

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

x+1=0 OR x-3=0

x=-1 OR x=3

We found that h(x)=0 for x=−1 or x=3. Since x=−1 doesn't make sense in our context, the only reasonable answer is x=3.

In conclusion, the stone will hit the water after 3 seconds.