Use the quadratic formula to solve the problem.
A soccer player throws the ball onto the field from the sideline. An equation modeling the ball's flight is h = -16t2 + 18t + 2. In how many seconds will the ball reach the ground?

Question

Use the quadratic formula to solve the problem.
A soccer player throws the ball onto the field from the sideline. An equation modeling the ball's flight is h = -16t2 + 18t + 2. In how many seconds will the ball reach the ground?

nurali · Answer

hits the ground when h = 0 and t > 0
-16t^2 + 18t + 2 = 0
Divide through by -2 => 8t^2 - 9t - 1 = 0
Quadratic formula again...
[ -(-9) +/- √(-9^2 - (4 * 8 * -1)) ] / (2 * 8)
[ 9 +/- √(81 + 32) ] / 16
[ 9 +/- √(81 + 32) ] / 16
[ 9 +/- √113 ] / 16
-0.1 or 1.23
It can't be -0.1 so the answer is 1.23