document.write( "Question 1054226: Solve for 0≤theta≤360, 2cos^2 theta +5cos theta-3=0 \n" ); document.write( "
Algebra.Com's Answer #669428 by ikleyn(52809)\"\" \"About 
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\n" ); document.write( "Solve for 0≤theta≤360, 2cos^2 theta +5cos theta-3=0
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document.write( "\"2cos%5E2%28theta%29+%2B5cos%28theta%29-3\" = 0,\r\n" );
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document.write( "Introduce new variable x = \"cos%28theta%29\". Then your equation takes the form\r\n" );
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document.write( "\"2x%5E2+%2B5x+-3%29%29%29\" = 0.\r\n" );
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document.write( "Apply the quadratic formula:\r\n" );
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document.write( "\"x%5B1%2C2%5D\" = \"%28-5+%2B-+sqrt%2825%2B4%2A2%2A3%29%29%2F%282%2A2%29\" = \"%28-5+%2B-+7%29%2F4\".\r\n" );
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document.write( "\"x%5B1%5D\" = \"1%2F2\",  \"x%5B2%5D\" = -3.\r\n" );
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document.write( "The second root is not acceptable, since cosine must be <= 1 by modulus.\r\n" );
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document.write( "The only solution is \"cos%28theta%29\" = \"1%2F2\",\r\n" );
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document.write( "which gives \"theta\" = 60 degs and/or  \"theta\" = 300 degs.\r\n" );
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document.write( "Answer.  \"theta\" = 60 degs  and/or  \"theta\" = 300 degs.\r\n" );
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