The equation $y = -4.9t^2 + 23.8t$ describes the height (in meters) of a projectile launched from the ground at 23.8 meters per second. In how many seconds will the projectile first reach 28 meters in height?
28 = -4.9t^2 + 23.8t
-4.9t^2 + 23.8t -28 = 0 quadratic formula to solve a = -4.9 b = 23.8 c = -28
\(t = {-b \pm \sqrt{b^2-4ac} \over 2a}\)
you'll get TWO t values ....one is for the time when proj is going up....the larger one is for when proj is coming down
