document.write( "Question 816667: let an be an arithmetic sequence. if a4=27 and a9=67, what is a1? \n" ); document.write( "
Algebra.Com's Answer #491656 by Edwin McCravy(20056)\"\" \"About 
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let an be an arithmetic sequence. if a4=27 and a9=67, what is a1?
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document.write( "an = a1 + (n-1)d\r\n" );
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document.write( "a4 = a1 + (4-1)d\r\n" );
document.write( "27 = a1 + 3d\r\n" );
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document.write( "a9 = a1 + (9-1)d\r\n" );
document.write( "67 = a1 + 8d\r\n" );
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document.write( "So we solve this system of equations:\r\n" );
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document.write( "27 = a1 + 3d\r\n" );
document.write( "67 = a1 + 8d\r\n" );
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document.write( "To eliminate d, multiply the first \r\n" );
document.write( "equation through by -8, and multiply\r\n" );
document.write( "the second equation through by 3\r\n" );
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document.write( "-216 = -8a1 - 24d\r\n" );
document.write( " 201 =  3a1 + 24d\r\n" );
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document.write( " -15 = -5a1\r\n" );
document.write( "   3 = a1\r\n" );
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document.write( "To check we find d by substituting\r\n" );
document.write( "3 for a1 in\r\n" );
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document.write( "27 = a1 + 3d\r\n" );
document.write( "27 = 3 + 3d\r\n" );
document.write( "24 = 3d\r\n" );
document.write( " 8 = d\r\n" );
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document.write( "So the sequence is found by starting with \r\n" );
document.write( "3 and adding 8 each time to get the next\r\n" );
document.write( "term:\r\n" );
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document.write( "3, 11, 19, 27, 35, 43, 51, 59, 67\r\n" );
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document.write( "Edwin
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