A ball is thrown from an initial height of 3 meters with an initial upward velocity of 20m/s. The ball's height (in meters) after seconds is given by the following h=3+20t-5t^2. Find all values of for which the ball's height is 13 meters.
+37157 h=3+20t-5t^2. looking for h = 13
13=3+20t-5t^2 re-arrange a bit
-5t2 +20t -10 = 0 divide by -5
t2 -4t +2 = 0 use Quadratic Formula
a = 1 b = -4 c = 2
\(t= {-4 \pm \sqrt{(-4)^2-4(1)(2)} \over 2(1)}\)
