Partial Decomposition Ca0Cdc
1. **State the problem:**
We want to find the partial fraction decomposition of the rational expression $$\frac{x^4 - 2x^3 + 8}{x^2(x - 2)}$$.
2. **Recall the formula and rules:**
For a rational expression where the denominator factors into powers of linear terms, the partial fraction decomposition takes the form:
$$\frac{P(x)}{(x)^2(x-2)} = \frac{A}{x} + \frac{B}{x^2} + \frac{C}{x-2}$$
where $A$, $B$, and $C$ are constants to be determined.
3. **Set up the equation:**
$$x^4 - 2x^3 + 8 = A x (x - 2) + B (x - 2) + C x^2$$
Multiply both sides by the denominator $x^2(x-2)$ to clear fractions.
4. **Expand the right side:**
$$A x (x - 2) = A (x^2 - 2x)$$
$$B (x - 2) = B x - 2B$$
$$C x^2 = C x^2$$
So,
$$A (x^2 - 2x) + B x - 2B + C x^2 = (A + C) x^2 + (B - 2A) x - 2B$$
5. **Equate coefficients with the left side:**
The left side is $$x^4 - 2x^3 + 8$$, which has terms of degree 4 and 3, but the right side only has up to degree 2. This means the original expression is an improper fraction and must be simplified by polynomial division first.
6. **Perform polynomial division:**
Divide $$x^4 - 2x^3 + 8$$ by $$x^2 (x - 2) = x^3 - 2x^2$$.
- First term: $$x^4 / x^3 = x$$
- Multiply divisor by $$x$$: $$x(x^3 - 2x^2) = x^4 - 2x^3$$
- Subtract: $$(x^4 - 2x^3 + 8) - (x^4 - 2x^3) = 8$$
Remainder is 8, so:
$$\frac{x^4 - 2x^3 + 8}{x^3 - 2x^2} = x + \frac{8}{x^3 - 2x^2} = x + \frac{8}{x^2 (x - 2)}$$
7. **Now decompose the proper fraction:**
$$\frac{8}{x^2 (x - 2)} = \frac{A}{x} + \frac{B}{x^2} + \frac{C}{x - 2}$$
8. **Multiply both sides by denominator:**
$$8 = A x (x - 2) + B (x - 2) + C x^2$$
9. **Expand right side:**
$$A (x^2 - 2x) + B x - 2B + C x^2 = (A + C) x^2 + (B - 2A) x - 2B$$
10. **Equate coefficients:**
Since left side is constant 8, coefficients of $x^2$ and $x$ must be zero:
- Coefficient of $x^2$: $$A + C = 0$$
- Coefficient of $x$: $$B - 2A = 0$$
- Constant term: $$-2B = 8$$
11. **Solve the system:**
From constant term:
$$-2B = 8 \implies B = -4$$
From $x$ term:
$$B - 2A = 0 \implies -4 - 2A = 0 \implies -2A = 4 \implies A = -2$$
From $x^2$ term:
$$A + C = 0 \implies -2 + C = 0 \implies C = 2$$
12. **Write the final decomposition:**
$$\frac{8}{x^2 (x - 2)} = \frac{-2}{x} + \frac{-4}{x^2} + \frac{2}{x - 2}$$
13. **Include the polynomial part from division:**
$$\frac{x^4 - 2x^3 + 8}{x^2 (x - 2)} = x - \frac{2}{x} - \frac{4}{x^2} + \frac{2}{x - 2}$$