document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=231484>Question 231484</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 6.8 #17\r<BR>\n" );
document.write( "\n" );
document.write( "Can someone please walk me through this?\r<BR>\n" );
document.write( "\n" );
document.write( "Before a football game, a coin toss is used to determine which team will kick off. The height h (in feet) of a coin above the ground t seconds after being flipped up into the air is given by the following equation. <BR>\n" );
document.write( "h = -16t2 + 22t + 20. \r<BR>\n" );
document.write( "\n" );
document.write( "How long does a team captain have to call heads or tails if it must be done while the coin is in the air?\r<BR>\n" );
document.write( "\n" );
document.write( "____ seconds\r<BR>\n" );
document.write( "\n" );
document.write( "Thank you,<BR>\n" );
document.write( "Alan </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #171303 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=171303\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Formula is:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "h = -16t^2 + 22t + 20.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "The amount of time he gets to call heads or tails is the amount of time that the coin is in the air.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "The coin is in the air until h = 0.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "At that point in time, the coin has touched the ground.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "You need to solve your equation for:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "-16t2 + 22t + 20 = 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Factor out a 2 from each coefficient to get:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "-8t^2 + 11t + 10 = 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Factors for this equation should be:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "(8t + 5) * (-t + 2)= 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "You get:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "-t = -2 which becomes t = 2\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "or you get:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "8t = -5 which you reject right away because it's negative, and t can't be negative.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Your answer should be t = 2\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "This means that he gets 2 seconds to call heads or tails before the coin hits the ground.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "To test, replace t in the original equation with 2 and you should get h = 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "h = -16t2 + 22t + 20 becomes:\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "h = -16*4 + 22*2 + 20 = -64 + 44 + 20 = -64 + 64 = 0\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "It checks out so your answer is 2 seconds.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "There is a more complicated answer but I don't think it's pertinent to the exercise so, for practical purposes, you can ignore that, and just use the formula as I showed you above.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );