Question 1138431
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. . . = cos(5x + 7x) = cos(12x).     <U>ANSWER</U>



Use the addition formula for cosine


    cos(a + b) = cos(a)*cos(b) - sin(a)*sin(b).


It is one of fundamental/basic formulas of trigonometry.
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On this formula, see the lessons

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF = http://www.algebra.com/algebra/homework/Trigonometry-basics/Addition-and-subtraction-formulas.lesson> Addition and subtraction formulas</A> 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF = http://www.algebra.com/algebra/homework/Trigonometry-basics/Addition-and-subtraction-formulas-Examples.lesson> Addition and subtraction formulas - Examples</A> 

in this site.