document.write( "Question 1202005: if $\"cos%28x%29+=+-5%2F13\"$ and $\"pi+%3C+x+%3C+3pi%2F2\"$ , find $\"cos%28x%2F2%29\"$ using half angle identities \n" ); document.write( "

Algebra.Com's Answer #836619 by Edwin McCravy(20065) $\"\"$ $\"About$

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document.write( "The identity to use is \r\n" );
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document.write( "Since we are finding  we divide all three sides of the domain for\r\n" );
document.write( "x by 2, so we'll have the domain for .\r\n" );
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document.write( ", divide through by 2: \r\n" );
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document.write( ", which in degrees is between 90^o and 135^o.\r\n" );
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document.write( "which means x/2 is in QII.  The cosine is negative in QII, so we use the\r\n" );
document.write( "negative sign\r\n" );
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document.write( "Multiply inside the square root radical by 13/13\r\n" );
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document.write( "You can rationalize the denominator of that if you like.\r\n" );
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document.write( "Edwin

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