document.write( "Question 357926: The sequence 3,a,b,c,768 is a geometric sequence. Find the values of a,b,and c. \n" ); document.write( "
Algebra.Com's Answer #255499 by Edwin McCravy(20064)\"\" \"About 
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3,a,b,c,768
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document.write( "Let the common ratio be r\r\n" );
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document.write( "\"a+=+3r\"\r\n" );
document.write( "\"b+=+ar+=+%283r%29r+=+3r%5E2\"\r\n" );
document.write( "\"c+=+br+=+%283r%5E2%29r+=+3r%5E3\"\r\n" );
document.write( "\"768+=+cr+=+%283r%5E3%29r+=+3r%5E4\"\r\n" );
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document.write( "\"768=3r%5E4\"\r\n" );
document.write( "Divide both sides by 3\r\n" );
document.write( "\"256=r%5E4\"\r\n" );
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document.write( "Use the principle of even roots:\r\n" );
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document.write( "\"%22%22+%2B-+root%284%2C256%29=r\"\r\n" );
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document.write( "\"%22%22+%2B-+4+=+r\"\r\n" );
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document.write( "If r = +4, then\r\n" );
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document.write( "a = 3r = 3(+4) = 12\r\n" );
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document.write( "b = ar = 12(+4) = 48\r\n" );
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document.write( "c = br = 48(+4) = 192\r\n" );
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document.write( "and as a check:\r\n" );
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document.write( "768 = cr = 192(4) = 768  so that checks.\r\n" );
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document.write( "So one solution is a=12, b = 48, c = 192\r\n" );
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document.write( "If r = -4, then\r\n" );
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document.write( "a = 3r = 3(-4) = -12\r\n" );
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document.write( "b = ar = -12(-4) = 48\r\n" );
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document.write( "c = br = 48(-4) = -192\r\n" );
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document.write( "and as a check:\r\n" );
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document.write( "768 = cr = -192(-13) = 768,so that checks too.\r\n" );
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document.write( "So the other solution is a=-12, b = 48, c = -192\r\n" );
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document.write( "There are two solutions.\r\n" );
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document.write( "Edwin
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