document.write( "Question 1036823: if (x+1/x)^2 = 3 then find the value of x^206 + x^200 + x^90 + x^84 + x^18 + x^12 + x^6 + 1 \n" ); document.write( "
Algebra.Com's Answer #651542 by ikleyn(52786)\"\" \"About 
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\n" ); document.write( "if (x+1/x)^2 = 3 then find the value of x^206 + x^200 + x^90 + x^84 + x^18 + x^12 + x^6 + 1
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\n" ); document.write( "\n" ); document.write( "Answer. If \"%28x%2B1%2Fx%29%5E2\" = \"3\" then the value of \"x%5E206+%2B+x%5E200+%2B+x%5E90+%2B+x%5E84+%2B+x%5E18+%2B+x%5E12+%2B+x%5E6+%2B+1\" is zero.\r
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document.write( "If  \"%28x%2B1%2Fx%29%5E2\" = \"3\"  then\r\n" );
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document.write( "\"x%5E2\" + \"2\" + \"1%2Fx%5E2\" = \"3\",\r\n" );
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document.write( "\"x%5E2\" + \"1%2Fx%5E2\" = \"1\",\r\n" );
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document.write( "\"x%5E2+-1+%2B+1%2Fx%5E2\" = \"0\",   ( <--- Introduce new variable u = \"x%5E2\" )  ---> \r\n" );
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document.write( "\"u+-+1+%2B+1%2Fu\" = \"0\",   ( <---multiply both sides by u)  ---> \r\n" );
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document.write( "\"u%5E2+-u+%2B+1\" = \"0\",    ( <--- solve by using the quadratic formula )  ---> \r\n" );
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document.write( "\"u%5B1%2C2%5D\" = \"1%2F2+%2B-+i%2A%28sqrt%283%29%2F2%29\" = \"cos%28pi%2F3%29+%2B-+i%2Asin%28pi%2F3%29%29\",   --->\r\n" );
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document.write( "\"x%5B1%2C2%5D\" = \"cos%28pi%2F6%29+%2B-+i%2Asin%28pi%2F6%29\".   ( since x = \"sqrt%28u%29\" )\r\n" );
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document.write( "In other words, if  \"%28x%2B1%2Fx%29%5E2\" = \"3\"  then x is the primitive root of the degree 12 of 1.\r\n" );
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document.write( "Then\r\n" );
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document.write( "\"x%5E90\" = \"-x%5E84\",  so  \"x%5E90+%2B+x%5E84\" = \"0\";\r\n" );
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document.write( "\"x%5E18\" = \"-x%5E12\",  so  \"x%5E18+%2B+x%5E12\" = \"0\";\r\n" );
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document.write( "\"x%5E6\" = \"-1\",  so  \"x%5E6+%2B+1\" = \"0\",  and also\r\n" );
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document.write( "\"x%5E206\" = \"-x%5E200\",  so  \"x%5E206+%2B+x%5E200\" = \"0\".\r\n" );
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document.write( "Hence,  the value of \"x%5E206+%2B+x%5E200+%2B+x%5E90+%2B+x%5E84+%2B+x%5E18+%2B+x%5E12+%2B+x%5E6+%2B+1\" is zero.\r\n" );
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Solved.\r
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