document.write( "Question 1154978: Robert threw a rock off a bridge into the river. The distance from the rock to the river is molded by the equation h=-16t^2-16t+60, where h is the height in ft. and t is the time in seconds. find out how long it took the rock to hit the surface. solve the equation by factoring. \n" ); document.write( "

Algebra.Com's Answer #777513 by MathLover1(20849) $\"\"$ $\"About$

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$\"h=-16t%5E2-16t%2B60\"$ , where $\"h\"$ is the height in $\"ft\"$ and $\"t\"$ is the time in seconds\r
\n" ); document.write( "\n" ); document.write( " the rock will hit the surface when $\"h=0\"$ \r
\n" ); document.write( "\n" ); document.write( "to find how long it will took the rock will hit the surface,plug in $\"h=0\"$ and solve for $\"t\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-16t%5E2-16t%2B60\"$ ........factor out $\"-4\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-4%284t%5E2%2B4t-15%29\"$ ...write $\"4t\"$ as $\"10t-6t\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-4%284t%5E2%2B10t-6t-15%29\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-4%28%284t%5E2%2B10t%29-%286t%2B15%29%29\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-4%282t%282t%2B5%29-3%282t%2B5%29%29\"$ \r
\n" ); document.write( "\n" ); document.write( " $\"0=-4%282t+-3%29%282t+%2B+5%29\"$ \r
\n" ); document.write( "\n" ); document.write( "solutions:
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\n" ); document.write( "if $\"0=%282t+-3%29\"$ => $\"2t=3\"$ => $\"t=3%2F2\"$ => $\"t=1.5\"$ \r
\n" ); document.write( "\n" ); document.write( "if $\"0=+%282t+%2B+5%29\"$ => $\"2t=-5\"$ => $\"t=-5%2F2\"$ => disregard negative solution\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "so, it took $\"1.5\"$ seconds the rock to hit the surface\r
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