A ball is projected into the air. Its height at time, t, is given by the equation: h = -16t2 + 50t + 2. When will the height be 6 feet the first time?

Question

the answers are:

A. 0.5 sec

B. 3.125 sec

C. 0.08 sec

D. 6.2 sec

Answer 1

-16t^2 +50t + 2 = 6

-8t^2 +25t -2 = 0

8t^2 -25t +2 = 0

use the quadratic formula with a=8, b=-25, c =2

t =-b/2a -(1/a)sqr(b^2-4ac)

t=25/16 -(1/16)sqr(625-64)

t = 25/16 - (1/16)sqr561

t = .0822 seconds

C is the best answer