SOLUTION: Write the expression as the sine or cosine of an angle. cos5xcos7x-sin5xsin7x

Question 1138431: Write the expression as the sine or cosine of an angle.
cos5xcos7x-sin5xsin7x
Answer by ikleyn(52830) (Show Source): You can put this solution on YOUR website!
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. . . = cos(5x + 7x) = cos(12x).     ANSWER



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
- Addition and subtraction formulas
- Addition and subtraction formulas - Examples
in this site.

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