SOLUTION: audrey uses a slingshot to shoot a marble from a window.The height of the marble h(t) in feet at a time t seconds is given by the function h(t)=-16t^2-62t + 188.How many seconds el

Question 706509: audrey uses a slingshot to shoot a marble from a window.The height of the marble h(t) in feet at a time t seconds is given by the function h(t)=-16t^2-62t + 188.How many seconds elapse before the marble hits the ground?
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
h(t)=-16t^2-62t + 188
when the marble hits the ground, the height is 0. Set h(t) to 0 and solve for t:
0=-16t^2-62t + 188
0=16t^2+62t-188
0=8t^2+31t-94
0=8t^2-16t+47t-94
0=(8t^2-16t)+(47t-94)
0=8t(t-2)+47(t-2)
0=(t-2)(8t+47)
t = {-47/8, 2}
throw out the negative value (extraneous) leaving:
t = 2 seconds

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