Find the partial fraction decomposition for the rational function.

In summary, the partial fraction decomposition for the given rational function is $\frac{-4}{x^2+2}+\frac{5}{x-9}$ with the values of $A=-4, B=5, C=1$.
  • #1
shamieh
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Find the partial fraction decomposition for the rational function.

\(\displaystyle \frac{-4x^2 - 8x - 19}{(x^2 + 2)(x-9)}\)

I'm not sure what to do.
 
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  • #2
shamieh said:
Find the partial fraction decomposition for the rational function.

\(\displaystyle \frac{-4x^2 - 8x - 19}{(x^2 + 2)(x-9)}\)

I'm not sure what to do.

$$\frac{-4x^2 - 8x - 19}{(x^2 + 2)(x-9)}=\frac{Ax+B}{x^2+2}+\frac{C}{x-9}$$

$$\frac{-4x^2 - 8x - 19}{(x^2 + 2)(x-9)}=\frac{(Ax+B)(x-9)+C(x^2+2)}{(x^2+2)(x-9)}$$

$$-4x^2 - 8x - 19=(Ax+B)(x-9)+C(x^2+2) \Rightarrow \\ -4x^2 - 8x - 19=Ax^2-9Ax+Bx-9B+Cx^2+2C \Rightarrow \\ -4x^2 - 8x - 19=(A+C)x^2+(B-9A)x+(2C-9B)$$

So $$-4=A+C, \ \ \ -8=B-9A, \ \ \ -19=2C-9B$$

Solving this system you will find the values of $A,B,C$.

Then substistute these values at $$\frac{Ax+B}{x^2+2}+\frac{C}{x-9}$$
 

FAQ: Find the partial fraction decomposition for the rational function.

What is a partial fraction decomposition?

A partial fraction decomposition is a process used to break down a rational function into simpler fractions, making it easier to integrate or manipulate. It involves expressing the rational function as a sum of simpler fractions with distinct denominators.

Why is partial fraction decomposition useful?

Partial fraction decomposition is useful in solving integrals and simplifying rational functions. It allows for more efficient manipulation and can also provide insight into the behavior of the function.

What is the general form of a partial fraction decomposition?

The general form of a partial fraction decomposition is: P(x)/Q(x) = A(x)/D(x) + B(x)/E(x) + ..., where P(x) and Q(x) are polynomials, A(x), B(x), etc. are constants or polynomials with smaller degree than their corresponding denominators, and D(x), E(x), etc. are distinct linear factors of Q(x).

How do you find the partial fraction decomposition for a rational function?

To find the partial fraction decomposition, you can follow these steps:

  • Factor the denominator Q(x) into linear factors
  • Write the partial fraction decomposition in the general form
  • Set up a system of equations using the coefficients of the decomposed fractions
  • Solve the system of equations to find the values of the constants or polynomials
  • Write the final decomposition using the values found in the previous step

Are there any special cases in partial fraction decomposition?

Yes, there are a few special cases in partial fraction decomposition, including when the degree of the numerator is equal to or greater than the degree of the denominator, when the denominator has repeated factors, and when the denominator has irreducible quadratic factors. These cases require additional steps and techniques in the decomposition process.

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