SOLUTION: a particle is projected from ground level so that its height above the ground after t second is given by 20 t-5t square meters. after how many seconds is it 15 meter above the grou

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Question 970736: a particle is projected from ground level so that its height above the ground after t second is given by 20 t-5t square meters. after how many seconds is it 15 meter above the ground? can you explain briefly why there are two possible answers?
Answer by macston(5194) About Me  (Show Source):
You can put this solution on YOUR website!
.
20t-5t%5E2=15
20t=5t%5E2%2B15
0=5t%5E2-20t%2B15
0=t%5E2-4t%2B3
0=%28t-3%29%28t-1%29
t-3=0 or t-1=0
t=3 or t=1
ANSWER:
The particle reaches 15 meters on the way up after 1 second,
and passes 15 meters again after 3 seconds on the way down.