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Partial Fractions Lesson 7.3, page 737 Objective: To decompose rational expressions into partial fractions.

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Presentation on theme: "Partial Fractions Lesson 7.3, page 737 Objective: To decompose rational expressions into partial fractions."— Presentation transcript:

1 Partial Fractions Lesson 7.3, page 737 Objective: To decompose rational expressions into partial fractions.

2 Review: Rational Expressions rational function – a quotient of two polynomials where p(x) and q(x) are polynomials and where q(x) is not the zero polynomial.

3 Review AddingSubtracting Rationals

4 Definition In the problem above, the fractions on the right are called “partial fractions”. In calculus, it is often helpful to write a rational expression as the sum of two or more simpler rational expressions.

5 What is decomposition of partial fractions? Writing a more complex fraction as the sum or difference of simpler fractions. Examples: Why would you ever want to do this? It’s EXTREMELY helpful in calculus!

6 Example 1 Decompose into partial fractions. Begin by factoring the denominator: (x + 2)(2x  3). We know that there are constants A and B such that To determine A and B, we add the expressions on the right…giving us…

7 Equate the numerators: 4x  13 = A(2x  3) + B(x + 2) Since the above equation containing A and B is true for all x, we can substitute any value of x and still have a true equation. If we choose x = 3/2, then 2x  3 = 0 and A will be eliminated when we make the substitution. This gives us 4(3/2)  13 = A[2(3/2)  3] + B(3/2 + 2)  7 = 0 + (7/2)B. B =  2.

8 If we choose x =  2, then x + 2 = 0 and B will be eliminated when we make the substitution. So, 4(  2)  13 = A[2(  2)  3] + B(  2 + 2)  21 =  7A. A = 3. The decomposition is as follows: Example 1 continued

9 Check Point 1, page 740 Find the partial fraction decomposition.

10 What if one on the denominators is a linear term squared? This is accounted for by having the nonsquared term as one denominator and having the squared term as another denominator. What if one denominator is a linear term cubed? There would be 3 denominators in the decomposition:

11 Example 2: Decompose into partial fractions.

12 Example 2 continued Next, we add the expression on the right: Then, we equate the numerators. This gives us Since the equation containing A, B, and C is true for all of x, we can substitute any value of x and still have a true equation. In order to have 2x – 1 = 0, we let x = ½. This gives us Solving, we obtain A = 5.

13 Example 2 continued In order to have x  2 = 0, we let x = 2. Substituting gives us To find B, we choose any value for x except ½ or 2 and replace A with 5 and C with  2. We let x = 1:

14 Example 2 continued The decomposition is as follows:

15 Check Point 2, page 741 Find the partial fraction decomposition.

16 Check Point 3, page 743 Find the partial fraction decomposition.


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