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Determine the following integrals by means of partial fractions: (x3+5x2-3x-1)/((3x+2)2(x2-1)) dx and (8x3-x2+4x-3)/((3-2x)3) dx

Mathematics

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Here are the solutions for the integrals using partial fractions:

Part 3.1· 4 steps

∫x3+5x2−3x−1(3x+2)2(x2−1)dx\int \frac{x^3 + 5x^2 - 3x - 1}{(3x+2)^2(x^2-1)} dx
  1. Factor the denominator completely and set up the partial fraction decomposition.

    The denominator is (3x+2)2(x2−1)=(3x+2)2(x−1)(x+1)(3x+2)^2(x^2-1) = (3x+2)^2(x-1)(x+1).
    The partial fraction decomposition is:

    x3+5x2−3x−1(3x+2)2(x−1)(x+1)=A3x+2+B(3x+2)2+Cx−1+Dx+1\frac{x^3 + 5x^2 - 3x - 1}{(3x+2)^2(x-1)(x+1)} = \frac{A}{3x+2} + \frac{B}{(3x+2)^2} + \frac{C}{x-1} + \frac{D}{x+1}

    Multiply both sides by the common denominator (3x+2)2(x−1)(x+1)(3x+2)^2(x-1)(x+1):

    x3+5x2−3x−1=A(3x+2)(x−1)(x+1)+B(x−1)(x+1)+C(3x+2)2(x+1)+D(3x+2)2(x−1)x^3 + 5x^2 - 3x - 1 = A(3x+2)(x-1)(x+1) + B(x-1)(x+1) + C(3x+2)^2(x+1) + D(3x+2)^2(x-1)
  2. Solve for the coefficients A, B, C, and D.

    • Set x=1x = 1: 13+5(1)2−3(1)−1=C(3(1)+2)2(1+1)1^3 + 5(1)^2 - 3(1) - 1 = C(3(1)+2)^2(1+1) 2=C(5)2(2)  ⟹  2=50C  ⟹  C=250=1252 = C(5)^2(2) \implies 2 = 50C \implies C = \frac{2}{50} = \frac{1}{25}

    • Set x=−1x = -1: (−1)3+5(−1)2−3(−1)−1=D(3(−1)+2)2(−1−1)(-1)^3 + 5(-1)^2 - 3(-1) - 1 = D(3(-1)+2)^2(-1-1) −1+5+3−1=D(−1)2(−2)  ⟹  6=−2D  ⟹  D=−3-1 + 5 + 3 - 1 = D(-1)^2(-2) \implies 6 = -2D \implies D = -3

    • Set x=−23x = -\frac{2}{3}: (−23)3+5(−23)2−3(−23)−1=B(−23−1)(−23+1)(-\frac{2}{3})^3 + 5(-\frac{2}{3})^2 - 3(-\frac{2}{3}) - 1 = B(-\frac{2}{3}-1)(-\frac{2}{3}+1) −827+209+2−1=B(−53)(13)-\frac{8}{27} + \frac{20}{9} + 2 - 1 = B(-\frac{5}{3})(\frac{1}{3}) −8+60+2727=−59B  ⟹  7927=−59B  ⟹  B=7927⋅(−95)=−7915\frac{-8 + 60 + 27}{27} = -\frac{5}{9}B \implies \frac{79}{27} = -\frac{5}{9}B \implies B = \frac{79}{27} \cdot (-\frac{9}{5}) = -\frac{79}{15}

    • Compare coefficients of x3x^3: The expanded equation is x3+5x2−3x−1=A(3x3+2x2−3x−2)+B(x2−1)+C(9x3+21x2+16x+4)+D(9x3+3x2−8x−4)x^3 + 5x^2 - 3x - 1 = A(3x^3 + 2x^2 - 3x - 2) + B(x^2-1) + C(9x^3+21x^2+16x+4) + D(9x^3+3x^2-8x-4). Comparing coefficients of x3x^3: 1=3A+9C+9D1 = 3A + 9C + 9D 1=3A+9(125)+9(−3)1 = 3A + 9(\frac{1}{25}) + 9(-3) 1=3A+925−27  ⟹  1=3A+9−67525  ⟹  1=3A−666251 = 3A + \frac{9}{25} - 27 \implies 1 = 3A + \frac{9 - 675}{25} \implies 1 = 3A - \frac{666}{25} 3A=1+66625=25+66625=69125  ⟹  A=691753A = 1 + \frac{666}{25} = \frac{25 + 666}{25} = \frac{691}{25} \implies A = \frac{691}{75}

  3. Integrate each term of the partial fraction decomposition.

    ∫(691/753x+2+−79/15(3x+2)2+1/25x−1+−3x+1)dx\int \left( \frac{691/75}{3x+2} + \frac{-79/15}{(3x+2)^2} + \frac{1/25}{x-1} + \frac{-3}{x+1} \right) dx =69175∫13x+2dx−7915∫(3x+2)−2dx+125∫1x−1dx−3∫1x+1dx= \frac{691}{75} \int \frac{1}{3x+2} dx - \frac{79}{15} \int (3x+2)^{-2} dx + \frac{1}{25} \int \frac{1}{x-1} dx - 3 \int \frac{1}{x+1} dx =69175(13ln⁡∣3x+2∣)−7915(13(3x+2)−1−1)+125ln⁡∣x−1∣−3ln⁡∣x+1∣+K= \frac{691}{75} \left(\frac{1}{3}\ln|3x+2|\right) - \frac{79}{15} \left(\frac{1}{3}\frac{(3x+2)^{-1}}{-1}\right) + \frac{1}{25}\ln|x-1| - 3\ln|x+1| + K
  4. Simplify and combine the results.

    691225ln⁡∣3x+2∣+7945(3x+2)+125ln⁡∣x−1∣−3ln⁡∣x+1∣+K\boxed{\frac{691}{225}\ln|3x+2| + \frac{79}{45(3x+2)} + \frac{1}{25}\ln|x-1| - 3\ln|x+1| + K}

Part 3.2· 4 steps

∫8x3−x2+4x−3(3−2x)3dx\int \frac{8x^3 - x^2 + 4x - 3}{(3-2x)^3} dx
  1. Use a substitution to simplify the denominator.

    Let u=3−2xu = 3-2x. Then 2x=3−u2x = 3-u, so x=3−u2x = \frac{3-u}{2}.
    Also, du=−2dxdu = -2 dx, which means dx=−12dudx = -\frac{1}{2} du.

  2. Substitute xx and dxdx into the integral and simplify the numerator.

    Numerator: 8x3−x2+4x−38x^3 - x^2 + 4x - 3

    =8(3−u2)3−(3−u2)2+4(3−u2)−3= 8\left(\frac{3-u}{2}\right)^3 - \left(\frac{3-u}{2}\right)^2 + 4\left(\frac{3-u}{2}\right) - 3 =8(3−u)38−(3−u)24+2(3−u)−3= 8\frac{(3-u)^3}{8} - \frac{(3-u)^2}{4} + 2(3-u) - 3 =(27−27u+9u2−u3)−14(9−6u+u2)+(6−2u)−3= (27 - 27u + 9u^2 - u^3) - \frac{1}{4}(9 - 6u + u^2) + (6 - 2u) - 3 =−u3+(9−14)u2+(−27+32−2)u+(27−94+6−3)= -u^3 + (9 - \frac{1}{4})u^2 + (-27 + \frac{3}{2} - 2)u + (27 - \frac{9}{4} + 6 - 3) =−u3+354u2−552u+1114= -u^3 + \frac{35}{4}u^2 - \frac{55}{2}u + \frac{111}{4}

    The integral becomes:

    ∫−u3+354u2−552u+1114u3(−12)du\int \frac{-u^3 + \frac{35}{4}u^2 - \frac{55}{2}u + \frac{111}{4}}{u^3} \left(-\frac{1}{2}\right) du =−12∫(−u3u3+35u24u3−55u2u3+1114u3)du= -\frac{1}{2} \int \left( \frac{-u^3}{u^3} + \frac{35u^2}{4u^3} - \frac{55u}{2u^3} + \frac{111}{4u^3} \right) du =−12∫(−1+354u−552u2+1114u3)du= -\frac{1}{2} \int \left( -1 + \frac{35}{4u} - \frac{55}{2u^2} + \frac{111}{4u^3} \right) du
  3. Integrate each term with respect to uu.

    =−12(−u+354ln⁡∣u∣−552(−1u)+1114(−12u2))+C= -\frac{1}{2} \left( -u + \frac{35}{4}\ln|u| - \frac{55}{2}\left(-\frac{1}{u}\right) + \frac{111}{4}\left(-\frac{1}{2u^2}\right) \right) + C =−12(−u+354ln⁡∣u∣+552u−1118u2)+C= -\frac{1}{2} \left( -u + \frac{35}{4}\ln|u| + \frac{55}{2u} - \frac{111}{8u^2} \right) + C =12u−358ln⁡∣u∣−554u+11116u2+C= \frac{1}{2}u - \frac{35}{8}\ln|u| - \frac{55}{4u} + \frac{111}{16u^2} + C
  4. Substitute back u=3−2xu = 3-2x.

    12(3−2x)−358ln⁡∣3−2x∣−554(3−2x)+11116(3−2x)2+C\boxed{\frac{1}{2}(3-2x) - \frac{35}{8}\ln|3-2x| - \frac{55}{4(3-2x)} + \frac{111}{16(3-2x)^2} + C}

    The constant term 32\frac{3}{2} from 12(3−2x)\frac{1}{2}(3-2x) can be absorbed into the integration constant CC.
    So, an equivalent form is:

    −x−358ln⁡∣3−2x∣−554(3−2x)+11116(3−2x)2+C\boxed{-x - \frac{35}{8}\ln|3-2x| - \frac{55}{4(3-2x)} + \frac{111}{16(3-2x)^2} + C}
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