its an algebra question

Question

a model rocket is fired straight up from the ground. the height h of the rocket (in feet) at any time t (in seconds) can be modeled by the equation h=-16t^2+160t. when will the height of the rocket be 336 feet at t

Answer 1

Set h=336 and solve for t.

 

336 = -16t² + 160t

 

 

Subtract 336 on both sides of the equation to get a quadratic equation.

 

0 = -16t² + 160t - 336

 

0 = -16(t² - 10 + 21)

 

 

Set the term in parenthesis equal to zero.

 

t² - 10t + 21 = 0

 

Factor using FOIL.

 

(t - 7)(t - 3) = 0

 

t = 7  ,   t = 3

 

 

Next, we need to use our logic to determine which value of t to accept.  The coefficient of t in the original equation represents the speed of the rocket at its launch.   Ask yourself this question:  Does it take the rocket less time to reach a height of 336 feet at that speed, or more time to reach a height of 336 feet?  Because of gravity, the rocket may take longer to reach its height.  So we accept the greater value of t.

 

 

Accept  t=7

 

The rocket will be at a height of 336 feet in 7 seconds.

Answer 2

Please use B^2 - 4ac

 

http://www.mathwords.com/d/discriminant_quadratic.htm

 

( I am solving it right now)

 

a quadratic equation.

 

D = b^2 - 4*a*c

 

D = (160)^2 - 4 * (-16) * (-1)

 

D = 25600 - 4 * (-16) * (-1)

 

D = 25536

 

Let me know if you got the same answer