document.write( "Question 1153160: If sin(x)+cos(x) = -1/5, and 3pi/4 ≤ x ≤ pi, find the value of cos(2x) \n" ); document.write( "

Algebra.Com's Answer #775347 by Edwin McCravy(20055) $\"\"$ $\"About$

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If sin(x)+cos(x) = -1/5, and 3pi/4 ≤ x ≤ pi, find the value of cos(2x)
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document.write( "Clear of fractions by multiplying thru by 5\r\n" );
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document.write( "Use identity \r\n" );
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document.write( "Isolate the term with the square root\r\n" );
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document.write( "Square both sides:\r\n" );
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document.write( "divide through by 2\r\n" );
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document.write( "Factor the right side\r\n" );
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document.write( "Use the zero-factor property\r\n" );
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document.write( "Since we are given \r\n" );
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document.write( "which means x is in QII where the sine is positive,\r\n" );
document.write( "we can eliminate the negative value for the sine.\r\n" );
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document.write( "Use identity\r\n" );
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document.write( "Edwin

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