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Solve a Trig Equation by Finding a Greatest Common Factor

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2016-03-26 20:21:12
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Trigonometry For Dummies
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The trigonometry equations that require finding a greatest common factor, factoring it out, and then solving the equation could look like one of the following two equations:

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Both of these equations are solved here.

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  1. Factor out sin x from each of the two terms.

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  2. Set the two different factors equal to 0.

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  3. Solve for the values of x that satisfy both equations. Use a scientific calculator.

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    All these values are solutions for the original equation. The complete list is x = 0°, 60°, 180°, 300°.

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  4. Move the term on the right to the left by subtracting it from each side.

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A common error in algebra — which could carry over in trig — is to divide each side by the common factor. You should never do that, because you’ll lose part of the solution.

  1. Factor out the cos x from each term.

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    You don’t want to divide each side by cos x, because you’ll lose a solution if you do.

  2. Set the two different factors equal to 0.

    image8.png
  3. Solve for the values of x that satisfy both equations.

    image9.png

    So the solutions are all of the form x = 90° + 180°n or x = 60° + 180°n.

About This Article

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Mary Jane Sterling (Peoria, Illinois) is the author of Algebra I For Dummies, Algebra Workbook For Dummies, Algebra II For Dummies, Algebra II Workbook For Dummies, and many other For Dummies books. She taught at Bradley University in Peoria, Illinois for more than 30 years, teaching algebra, business calculus, geometry, and finite mathematics.