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.

Guest Feb 15, 2021

#1**+1 **

h=3+20t-5t^2. looking for h = 13

13=3+20t-5t^2 re-arrange a bit

-5t^{2 }+20t -10 = 0 divide by -5

t^{2} -4t +2 = 0 use Quadratic Formula

a = 1 b = -4 c = 2

\(t= {-4 \pm \sqrt{(-4)^2-4(1)(2)} \over 2(1)}\)

ElectricPavlov Feb 15, 2021