document.write( "Question 682133: Hello,\r
\n" ); document.write( "\n" ); document.write( "I wanted to see if I was doing this problem correctly.\r
\n" ); document.write( "\n" ); document.write( "I started the answer with -16t^2+16t+410=90, then subtracted 90 to get -16t^2+16t+320=0 and then perform the quadratic equation to get the answer. Is this the right start?\r
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\n" ); document.write( "\n" ); document.write( "The function h(t) = -16^2+16t+410 gives the height h, in feet, of a coin tossed upward from a balcony 410 ft high with an initial velocity of 16 ft/sec. During what interval of time will the coin be at a height of at least 90 ft? \r
\n" ); document.write( "\n" ); document.write( "Thanks \n" ); document.write( "
Algebra.Com's Answer #423051 by nerdybill(7384)\"\" \"About 
You can put this solution on YOUR website!
I started the answer with -16t^2+16t+410=90, then subtracted 90 to get -16t^2+16t+320=0 and then perform the quadratic equation to get the answer. Is this the right start?
\n" ); document.write( "Yes, applying the \"quadratic equation\" is one approach.
\n" ); document.write( "But, you could have \"factored\" it (an easier approach):
\n" ); document.write( "-16t^2+16t+320=0
\n" ); document.write( "dividing both sides by -16:
\n" ); document.write( "t^2-t-20=0
\n" ); document.write( "factoring:
\n" ); document.write( "(t+4)(t-5) = 0
\n" ); document.write( "t = {-4, 5}
\n" ); document.write( "throw away the negative solution (extraneous) leaving:
\n" ); document.write( "t = 5 seconds
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