document.write( "Question 151528: If a skydiver jumps from a airplane at a height of 8,256 ft, then for the first 5 seconds, her height above the earth is approximated by the formula, h= -16t^2 + 8,256. How many seconds does it take her to reach 8,000 ft? \n" ); document.write( "

Algebra.Com's Answer #111385 by Earlsdon(6294) $\"\"$ $\"About$

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Starting with the given equation: $\"h+=+-16t%5E2%2B8256\"$ , you want to find at what time, t, will h = 8000.
\n" ); document.write( " $\"8000+=+-16t%5E2%2B8256\"$ Subtract 8000 from both sides.
\n" ); document.write( " $\"-16t%5E2%2B256+=+0\"$ Multiply through by -1.
\n" ); document.write( " $\"16t%5E2-256+=+0\"$ Notice that the binomial is the difference of squares, so you can factor this nicely...
\n" ); document.write( " $\"%284t-16%29%284t%2B16%29+=+0\"$ Now apply the zero products rule.
\n" ); document.write( " $\"4t-16+=+0\"$ or $\"4t%2B16+=+0\"$
\n" ); document.write( "If $\"4t-16+=+0\"$ then $\"4t+=+16\"$ and $\"t+=+4\"$
\n" ); document.write( "If $\"4t%2B16+=+0\"$ then $\"4t+=+-16\"$ and $\"t+=+-4\"$
\n" ); document.write( "Discard the negative answer because the time, t, should be positive.
\n" ); document.write( "It take 4 second for the skydiver to reach a height of 8,000 feet. \n" ); document.write( "

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