document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=864335>Question 864335</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A firecracker is fired straight up into the air out of a window of a building. Its height, in feet, is given by h = -16 t^2 + 88 t + 230, where t is the time, in seconds, the fircracker has been in the air. \r<BR>\n" );
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document.write( "When does it reaches a height of 350 feet? </SPAN>\n" );
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document.write( "(1) h = -16t^2 + 88t +230 and we want to know the t when h = 350. So let h = 350 and get<BR>\n" );
document.write( "(2) 350 = -16t^2 + 88t +230  or<BR>\n" );
document.write( "(3) -16t^2 + 88t +230 - 350 = 0 or<BR>\n" );
document.write( "(4) -16t^2 + 88t - 120 = 0 or<BR>\n" );
document.write( "(5) -2t^2 + 11t - 15 = 0<BR>\n" );
document.write( "Now use the quadratic solution formula to get<BR>\n" );
document.write( "(6) t = (11 +- 1)/4 or<BR>\n" );
document.write( "(7) t = {3,2.5}<BR>\n" );
document.write( "Let t = 3 in (1) to check the answer.<BR>\n" );
document.write( "Is (350 = -16*3^2 + 88*3 + 230)?<BR>\n" );
document.write( "Is (350 = -16*9 + 264 + 230)?<BR>\n" );
document.write( "Is (350 = 494 - 144)?<BR>\n" );
document.write( "Is (350 = 350)? Yes<BR>\n" );
document.write( "Answer: The firecracker reaches 350 ft at t = 2.5 seconds and 3 seconds. Note it reaches a peak of 351 ft at 2.75 seconds (half way between 2.5 and 3).<BR>\n" );
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