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Express (5x-2)/(x3(x+2)) in partial fraction.

Mathematics

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1. Express 5x−2x3(x+2)\frac{5x-2}{x^3(x+2)} in partial fraction.

  1. Set up the partial fraction decomposition.

    The denominator has a repeated linear factor x3x^3 and a distinct linear factor (x+2)(x+2).

    5x−2x3(x+2)=Ax+Bx2+Cx3+Dx+2\frac{5x-2}{x^3(x+2)} = \frac{A}{x} + \frac{B}{x^2} + \frac{C}{x^3} + \frac{D}{x+2}
  2. Multiply both sides by the common denominator x3(x+2)x^3(x+2).

    5x−2=Ax2(x+2)+Bx(x+2)+C(x+2)+Dx35x-2 = A x^2(x+2) + B x(x+2) + C(x+2) + D x^3
  3. Expand the right side and group terms by powers of xx.

    5x−2=A(x3+2x2)+B(x2+2x)+C(x+2)+Dx35x-2 = A(x^3+2x^2) + B(x^2+2x) + C(x+2) + D x^3 5x−2=Ax3+2Ax2+Bx2+2Bx+Cx+2C+Dx35x-2 = Ax^3+2Ax^2 + Bx^2+2Bx + Cx+2C + Dx^3 5x−2=(A+D)x3+(2A+B)x2+(2B+C)x+2C5x-2 = (A+D)x^3 + (2A+B)x^2 + (2B+C)x + 2C
  4. Equate coefficients of corresponding powers of xx.

    For x3x^3: A+D=0(1)A+D = 0 \quad (1)
    For x2x^2: 2A+B=0(2)2A+B = 0 \quad (2)
    For x1x^1: 2B+C=5(3)2B+C = 5 \quad (3)
    For x0x^0 (constant): 2C=−2(4)2C = -2 \quad (4)

  5. Solve the system of equations.

    From (4): C=−1C = -1.
    Substitute C=−1C=-1 into (3): 2B+(−1)=5  ⟹  2B=6  ⟹  B=32B + (-1) = 5 \implies 2B = 6 \implies B = 3.
    Substitute B=3B=3 into (2): 2A+3=0  ⟹  2A=−3  ⟹  A=−322A + 3 = 0 \implies 2A = -3 \implies A = -\frac{3}{2}.
    Substitute A=−32A=-\frac{3}{2} into (1): −32+D=0  ⟹  D=32-\frac{3}{2} + D = 0 \implies D = \frac{3}{2}.

  6. Write the partial fraction decomposition.

    5x−2x3(x+2)=−32x+3x2+−1x3+32x+2\frac{5x-2}{x^3(x+2)} = \frac{-\frac{3}{2}}{x} + \frac{3}{x^2} + \frac{-1}{x^3} + \frac{\frac{3}{2}}{x+2} 5x−2x3(x+2)=−32x+3x2−1x3+32(x+2)\frac{5x-2}{x^3(x+2)} = -\frac{3}{2x} + \frac{3}{x^2} - \frac{1}{x^3} + \frac{3}{2(x+2)}

    The final answer is −32x+3x2−1x3+32(x+2)\boxed{-\frac{3}{2x} + \frac{3}{x^2} - \frac{1}{x^3} + \frac{3}{2(x+2)}}.

    2. Integrate ∫5x−2x3(x+2) dx\int \frac{5x-2}{x^3(x+2)}\,dx.

  7. Use the partial fraction decomposition from the previous problem.

    ∫5x−2x3(x+2) dx=∫(−32x+3x2−1x3+32(x+2)) dx\int \frac{5x-2}{x^3(x+2)}\,dx = \int \left(-\frac{3}{2x} + \frac{3}{x^2} - \frac{1}{x^3} + \frac{3}{2(x+2)}\right)\,dx
  8. Integrate each term.

    Recall that ∫xn dx=xn+1n+1+K\int x^n\,dx = \frac{x^{n+1}}{n+1} + K for n≠−1n \ne -1, and ∫1x dx=ln⁡∣x∣+K\int \frac{1}{x}\,dx = \ln|x| + K.

    ∫−32x dx=−32ln⁡∣x∣\int -\frac{3}{2x}\,dx = -\frac{3}{2}\ln|x| ∫3x2 dx=∫3x−2 dx=3x−1−1=−3x\int \frac{3}{x^2}\,dx = \int 3x^{-2}\,dx = 3\frac{x^{-1}}{-1} = -\frac{3}{x} ∫−1x3 dx=∫−x−3 dx=−x−2−2=12x2\int -\frac{1}{x^3}\,dx = \int -x^{-3}\,dx = -\frac{x^{-2}}{-2} = \frac{1}{2x^2} ∫32(x+2) dx=32ln⁡∣x+2∣\int \frac{3}{2(x+2)}\,dx = \frac{3}{2}\ln|x+2|
  9. Combine the results and add the constant of integration KK.

    −32ln⁡∣x∣−3x+12x2+32ln⁡∣x+2∣+K-\frac{3}{2}\ln|x| - \frac{3}{x} + \frac{1}{2x^2} + \frac{3}{2}\ln|x+2| + K

    This can be rewritten using logarithm properties ln⁡a−ln⁡b=ln⁡ab\ln a - \ln b = \ln \frac{a}{b}:

    32(ln⁡∣x+2∣−ln⁡∣x∣)−3x+12x2+K\frac{3}{2}(\ln|x+2| - \ln|x|) - \frac{3}{x} + \frac{1}{2x^2} + K 32ln⁡∣x+2x∣−3x+12x2+K\frac{3}{2}\ln\left|\frac{x+2}{x}\right| - \frac{3}{x} + \frac{1}{2x^2} + K

    The final answer is 32ln⁡∣x+2x∣−3x+12x2+K\boxed{\frac{3}{2}\ln\left|\frac{x+2}{x}\right| - \frac{3}{x} + \frac{1}{2x^2} + K}.

    3. Solve x+1x−1≥2\frac{x+1}{x-1} \ge 2.

  10. Move all terms to one side to get a single fraction.

    x+1x−1−2≥0\frac{x+1}{x-1} - 2 \ge 0
  11. Find a common denominator and combine the terms.

    x+1x−1−2(x−1)x−1≥0\frac{x+1}{x-1} - \frac{2(x-1)}{x-1} \ge 0 x+1−(2x−2)x−1≥0\frac{x+1 - (2x-2)}{x-1} \ge 0 x+1−2x+2x−1≥0\frac{x+1 - 2x + 2}{x-1} \ge 0 −x+3x−1≥0\frac{-x+3}{x-1} \ge 0
  12. Identify the critical points where the numerator or denominator is zero.

    Numerator: −x+3=0  ⟹  x=3-x+3 = 0 \implies x = 3
    Denominator: x−1=0  ⟹  x=1x-1 = 0 \implies x = 1
    Note that x≠1x \ne 1 because the denominator cannot be zero.

  13. Test intervals defined by the critical points (−∞,1)(-\infty, 1), (1,3](1, 3], and [3,∞)[3, \infty).

    • For x<1x < 1 (e.g., x=0x=0): −0+30−1=3−1=−3\frac{-0+3}{0-1} = \frac{3}{-1} = -3. This is not ≥0\ge 0.
    • For 1<x≤31 < x \le 3 (e.g., x=2x=2): −2+32−1=11=1\frac{-2+3}{2-1} = \frac{1}{1} = 1. This is ≥0\ge 0. So, this interval is part of the solution.
    • For x>3x > 3 (e.g., x=4x=4): −4+34−1=−13\frac{-4+3}{4-1} = \frac{-1}{3}. This is not ≥0\ge 0.
  14. Write the solution.

    The inequality holds for 1<x≤31 < x \le 3.
    The final answer is 1<x≤3\boxed{1 < x \le 3}.

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