document.write( "Question 1138431: Write the expression as the sine or cosine of an angle.
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Algebra.Com's Answer #756228 by ikleyn(52840) $\"\"$ $\"About$

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document.write( ". . . = cos(5x + 7x) = cos(12x).     ANSWER\r\n" );
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document.write( "Use the addition formula for cosine\r\n" );
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document.write( "    cos(a + b) = cos(a)*cos(b) - sin(a)*sin(b).\r\n" );
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document.write( "It is one of fundamental/basic formulas of trigonometry.\r\n" );
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\n" ); document.write( "\n" ); document.write( "On this formula, see the lessons\r
\n" ); document.write( "\n" ); document.write( " - Addition and subtraction formulas \r
\n" ); document.write( "\n" ); document.write( " - Addition and subtraction formulas - Examples \r
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