# 6.2 Integration by Substitution M.L.King Jr. Birthplace, Atlanta, GA Greg Kelly Hanford High School Richland, Washington Photo by Vickie Kelly, 2002.

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6.2 Integration by Substitution M.L.King Jr. Birthplace, Atlanta, GA Greg Kelly Hanford High School Richland, Washington Photo by Vickie Kelly, 2002

The chain rule allows us to differentiate a wide variety of functions, but we are able to find antiderivatives for only a limited range of functions. We can sometimes use substitution to rewrite functions in a form that we can integrate.

Example 1: The variable of integration must match the variable in the expression. Dont forget to substitute the value for u back into the problem!

Example: (Exploration 1 in the book) One of the clues that we look for is if we can find a function and its derivative in the integrand. The derivative of is.Note that this only worked because of the 2x in the original. Many integrals can not be done by substitution.

Example 2: Solve for dx.

Example 3:

Example: (Not in book) We solve for because we can find it in the integrand.

Example 7:

Example 8: The technique is a little different for definite integrals. We can find new limits, and then we dont have to substitute back. new limit We could have substituted back and used the original limits.

Example 8: Wrong! The limits dont match! Using the original limits: Leave the limits out until you substitute back. This is usually more work than finding new limits

Example: (Exploration 2 in the book) Dont forget to use the new limits.

Until then, remember that half the AP exam and half the nations college professors do not allow calculators. In another generation or so, we might be able to use the calculator to find all integrals. You must practice finding integrals by hand until you are good at it!

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