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Determine the following integrals by means of partial fractions: 3.1 ∫(5x³ - x² + 8x - 4) / ((1-x)² (2x + 1)²) dx 3.2 ∫(4x³ - 6x² + 5x - 4) / (2x² + x - 6) dx

Mathematics

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Step 1: Perform polynomial long division for integral 3.2.
For integral 3.2, the degree of the numerator (4x3−6x2+5x−44x^3 - 6x^2 + 5x - 4) is 3, and the degree of the denominator (2x2+x−62x^2 + x - 6) is 2. Since the numerator's degree is greater than or equal to the denominator's degree, we must perform polynomial long division first.

\multicolumn2r2x−4\cline2−52x2+x−64x3−6x2+5x−4\multicolumn2r−(4x3+2x2−12x)\cline2−4\multicolumn2r0−8x2+17x−4\multicolumn2r−(−8x2−4x+24)\cline3−5\multicolumn2r021x−28\begin{array}{c|cc cc} \multicolumn{2}{r}{2x} & -4 \\ \cline{2-5} 2x^2+x-6 & 4x^3 & -6x^2 & +5x & -4 \\ \multicolumn{2}{r}{-(4x^3} & +2x^2 & -12x) \\ \cline{2-4} \multicolumn{2}{r}{0} & -8x^2 & +17x & -4 \\ \multicolumn{2}{r}{} & -(-8x^2 & -4x & +24) \\ \cline{3-5} \multicolumn{2}{r}{} & 0 & 21x & -28 \\ \end{array}

So, 4x3−6x2+5x−42x2+x−6=2x−4+21x−282x2+x−6\frac{4x^3 - 6x^2 + 5x - 4}{2x^2 + x - 6} = 2x - 4 + \frac{21x - 28}{2x^2 + x - 6}.

Step 2: Factor the denominator for integral 3.2.
The denominator is 2x2+x−62x^2 + x - 6. We find the roots using the quadratic formula x=−b±b2−4ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}:

x=−1±12−4(2)(−6)2(2)=−1±1+484=−1±494=−1±74x = \frac{-1 \pm \sqrt{1^2 - 4(2)(-6)}}{2(2)} = \frac{-1 \pm \sqrt{1 + 48}}{4} = \frac{-1 \pm \sqrt{49}}{4} = \frac{-1 \pm 7}{4}

The roots are x1=−1+74=64=32x_1 = \frac{-1+7}{4} = \frac{6}{4} = \frac{3}{2} and x2=−1−74=−84=−2x_2 = \frac{-1-7}{4} = \frac{-8}{4} = -2.
So, 2x2+x−6=2(x−32)(x+2)=(2x−3)(x+2)2x^2 + x - 6 = 2(x - \frac{3}{2})(x + 2) = (2x - 3)(x + 2).

Step 3: Decompose the remainder term into partial fractions for integral 3.2.
We set up the partial fraction decomposition for 21x−28(2x−3)(x+2)\frac{21x - 28}{(2x - 3)(x + 2)}:

21x−28(2x−3)(x+2)=A2x−3+Bx+2\frac{21x - 28}{(2x - 3)(x + 2)} = \frac{A}{2x - 3} + \frac{B}{x + 2}

Multiply both sides by (2x−3)(x+2)(2x - 3)(x + 2):

21x−28=A(x+2)+B(2x−3)21x - 28 = A(x + 2) + B(2x - 3)

To find AA, set x=32x = \frac{3}{2}:

21(32)−28=A(32+2)+B(0)21\left(\frac{3}{2}\right) - 28 = A\left(\frac{3}{2} + 2\right) + B(0) 632−562=A(72)\frac{63}{2} - \frac{56}{2} = A\left(\frac{7}{2}\right)
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