Trigonometry Workbook For Dummies
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With the trigonometric substitution method, you can do integrals containing radicals of certain forms because they match up with trigonometric functions. A sine can take the place of a radical in a particular form.

  1. Draw a right triangle where


    You should confirm this with the Pythagorean theorem.

  2. Solve


    differentiate, and solve for dx.

  3. Find which trig function equals the radical over the a, and then solve for the radical.

    Look at the triangle in the figure.

  4. Use the results from Steps 2 and 3 to make substitutions in the original problem and then integrate.

    Note that in this particular problem, you have to make three substitutions, not just two like in the first example.

  5. The triangle shows that


    Now, substitute back for your final answer.


It’s a walk in the park.

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

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