Question 236861
 the height of an object projected upward from ground level is given by {{{h=-16t^2+128t}}} where h is in feet and t is time in seconds. when will the object be 240 feet above ground level ... 

please help i dont understand
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{{{h=-16t^2+128t}}}

Substitute 240 ft as the height h in the equation:

{{{240=-16t^2+128t}}}

Get 0 on the right:  

{{{16t^2-128t+240=0}}}

Divide every term by {{{16}}}

{{{(16t^2)/16-(128t)/16+240/16=0}}}

{{{t^2-8t+15=0}}}

Factor the left side:

{{{(t-3)(t-5)=0}}}

Set each factor = 0

Setting {{{t-3=0}}
        {{{t=3}}} 

Setting {{{t-5=0}}}
        {{{t=5}}}

There are two solutions, because the
object will be exactly 240 feet above
the ground on its way UP exactly 3 
seconds after it is projected upward. 
Then it will be 240 feet above the ground 
again on its way back DOWN 5 seconds 
after it is projected upward.  So the 
answer is both 3 seconds and 5 seconds
after it is projected upward.

Edwin</pre>