quick question

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sportsstar469

Junior Member
Joined
Jul 7, 2009
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ok so i was given the opportunity to correct my math test to bring my grade up from an 88 to a 90. i just did the problem but im not sure if it is right. i got two answers so i am confused. i know yo ucant have a negative distance so im thinking one of the solutions is not right.

PROBLEM- A projectile is shot upward with an initial velocity of 48 feet per second and is released 64 feet above the ground. its height h after t seconds is modeled by the function:
h(t)=16t^2+48t+64
find when the projectile will hit the ground

ok first off i want to say i used the variable x instead of t because t confuses me with the plus signs.

i did 0= -16^2+48x+64
factored that out to.... 0= -16(x^2-3x-4)
then i got -16(x+1)(x-4)
-16 =0 which is false so i crossed it out
x+1=0 which is x = -1
and x-4=0 which is x=4

so my solutions are at 4seconds and at -1 seconds. would i cross out -1? I HAVE TO GET THIS EXTRA CREDIT.
 
sportsstar469 said:
ok so i was given the opportunity to correct my math test to bring my grade up from an 88 to a 90. i just did the problem but im not sure if it is right. i got two answers so i am confused. i know yo ucant have a negative distance so im thinking one of the solutions is not right.

PROBLEM- A projectile is shot upward with an initial velocity of 48 feet per second and is released 64 feet above the ground. its height h after t seconds is modeled by the function:
h(t)=16t^2+48t+64
find when the projectile will hit the ground---->Find the time it needs to hit the ground ?

ok first off i want to say i used the variable x instead of t because t confuses me with the plus signs.

i did 0= -16^2+48x+64
factored that out to.... 0= -16(x^2-3x-4)
then i got -16(x+1)(x-4)
-16 =0 which is false so i crossed it out
x+1=0 which is x = -1
and x-4=0 which is x=4

so my solutiuons are at 4 feet and at -1 feet. would i cross out -1? I HAVE TO GET THIS EXTRA CREDIOT.
Click to expand...
 
yeah i accidentally typed distance but you didnt even answer my question....
which :!: one of those solutions is correct.
 
Since you were asked please to clarify the question, clearly the poster did not feel confident in his understanding of your meaning. Surely you would prefer people wait to help with answers until after they are sure of the questions...? :roll:
 
Throw out -1 ,Since The solution is from one seconds before launch, which doesn't make sense in this context .
 
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