document.write( "Question 81396: In 1981 Vladameir set a world record of 19ft3/4 inch for the pole vault. To reach that height he obtained a speed of approx. 36ft per second on the runway. The formula h=-16t^2+36t gives his height t seconds after leaving the ground. Use the formula to find the exact values of t for which his height was 18 ft. \n" ); document.write( "

Algebra.Com's Answer #58430 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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n 1981 Vladameir set a world record of 19ft3/4 inch for the pole vault. To reach that height he obtained a speed of approx. 36ft per second on the runway. The formula h=-16t^2+36t gives his height t seconds after leaving the ground. Use the formula to find the exact values of t for which his height was 18 ft.
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\n" ); document.write( "Replace h with 18 and find t:
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\n" ); document.write( "-16t^2 + 36t = 18
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\n" ); document.write( "-16t^2 + 36t - 18 = 0; subtracted 18 from both sides, now a quadratic equation
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\n" ); document.write( "Simplify, divide equation by -2
\n" ); document.write( "+8t^2 - 18t + 9 = 0
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\n" ); document.write( "Use the quadratic equation to find t: a=8; b=-18; c=9:
\n" ); document.write( " $\"t+=+%28-%28-18%29+%2B-+sqrt%28+-18%5E2+-+4%2A+8+%2A+9+%29%29%2F%282%2A8%29+\"$
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\n" ); document.write( " $\"t+=+%28%2B18+%2B-+sqrt%28324+-+288+%29%29%2F%2816%29+\"$
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\n" ); document.write( "Do the math here, you should get two solutions. (0n the way up and on the way down) t = .75 sec and t = 1.5 sec
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