A rock is thrown in the air from the edge of a seaside cliff. Its height in feet is represented by f(x) = –16(x2 – 3x – 18), where x is the number of seconds since the rock was thrown. The height of the rock is 0 feet when it hits the water.How long does it take the rock to hit the water? How many seconds?
Accepted Solution
A:
Set the given equation equal to zero (0), since that's the height of the rock when it hits the water:
0 = -16(x^2 - 3x - 18) (Note: Please write x^2 to denote "square of x.")
Solving this equation for x, we get:
0 = -16(x-6)(x+3), and x=-3 or x=6. Since x represents time, discard the negative value x=-3.