document.write( "Question 871515: Five years later a boy's age will be 4 times the square of what it was 9 years ago. Find his present age. \n" ); document.write( "
Algebra.Com's Answer #525571 by Edwin McCravy(20056)\"\" \"About 
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document.write( "x       = the boy's age now\r\n" );
document.write( "x+5     = the boy's age five years later\r\n" );
document.write( "x-9     = what the boy's age was 9 years ago\r\n" );
document.write( "(x-9)²  = the square of what it was 9 years ago  \r\n" );
document.write( "4(x-9)² = 4 times the square of what it was 9 years ago\r\n" );
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document.write( "      x+5 = 4(x-9)²\r\n" );
document.write( "      x+5 = 4(x-9)(x-9)\r\n" );
document.write( "      x+5 = 4(x²-9x-9x+81)\r\n" );
document.write( "      x+5 = 4(x²-18x+81)\r\n" );
document.write( "      x+5 = 4x²-72x+324\r\n" );
document.write( "        0 = 4x²-73x+319\r\n" );
document.write( "        0 = (4x-29)(x-11)\r\n" );
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document.write( "     4x-29 =  0;    x-11 =  0\r\n" );
document.write( "        4x = 29        x = 11  \r\n" );
document.write( "         x = \"7%261%2F4\"      \r\n" );
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document.write( "He couldn't have been \"7%261%2F4\" years old since \r\n" );
document.write( "9 years ago he wouldn't have even been born.  So\r\n" );
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document.write( "The boy's present age = 11\r\n" );
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document.write( "Checking:\r\n" );
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document.write( "Five years later the boy's age will be 16, which will be \r\n" );
document.write( "4 times the square of what it was 9 years ago.  9 years\r\n" );
document.write( "ago, his age was 2.  The square of 2 is 4, and indeed \r\n" );
document.write( "16 is 4 times 4.\r\n" );
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document.write( "Edwin
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