SOLUTION: An arrow is launched upward. After t seconds,it's height(h) id given by the formula h=-16t+208t. After how many seconds will its height be 640 feet? Should this be solved using th

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Question 34690This question is from textbook intermediate algebra
: An arrow is launched upward. After t seconds,it's height(h) id given by the formula h=-16t+208t. After how many seconds will its height be 640 feet?
Should this be solved using the zero-factor theorem? How should I set it up?
This question is from textbook intermediate algebra

Answer by longjonsilver(2297)   (Show Source): You can put this solution on YOUR website!
i think you meant to have: ?

If so, then when height is 640, we get:




(t-8)(t-5) = 0
so t-8=0 or t-5=0
so t=5 or t=8

Two answers since the arrow reaches 640feet after 5 seconds, going up, then a further 3 seconds (the 8 seconds) it is again at 640 feet, coming down.

jon.