document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1125996>Question 1125996</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A rock is thrown upward from a bridge into a river below. The function f(t)=-16t^2+38t+90 determines the height of the rock above the surface of the water (in feet) in terms of the number of seconds t since the rock was thrown. \r<BR>\n" );
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document.write( "a. What is the bridge's height above the water?\r<BR>\n" );
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document.write( "b. How many seconds after being thrown does the rock hit the water?\r<BR>\n" );
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document.write( "c. How many seconds after being thrown does the rock reach its maximum height above the water?\r<BR>\n" );
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document.write( "d. What is the rock's maximum height above the water? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #742329 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=742329\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The height is 90 feet, the constant in the equation<BR>\n" );
document.write( "maximum height is where t=-b/2a of the quadratic or -38/-32 or t=19/16 sec<BR>\n" );
document.write( "putting that into the equation, height max is 112.6 feet\r<BR>\n" );
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document.write( "set it equal to 0 to find the landing time<BR>\n" );
document.write( "16t^2-38t-90=0, rewriting with positive first term<BR>\n" );
document.write( "t=(1/32)(38+/- sqrt (1444+5760)0; sqrt 7200=84.85<BR>\n" );
document.write( "t=3.84 sec until it hits the water\r<BR>\n" );
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