9514 1404 393
Answer:
t = 3-√7 and 3+√7 seconds after launch
Explanation:
You want to find the values of t that make h=10.
10 = 30t -5t^2
t^2 -6t = -2 . . . . . divide by -5
t^2 -6t +9 = 7 . . . add 9 to complete the square
(t -3)^2 = 7 . . . . . write as a square
t -3 = ±√7 . . . . . . take the square root
t = 3 ±√7 . . . . . . values of t for which height is 10 meters
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These values are about 0.354 seconds, and 5.646 seconds.