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Decompose the following rational expression into partial fractions: (2x-7)/(25x - 24 - 6x2)

Mathematics

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Answer

−57(8−3x)−87(2x−3)-\frac{5}{7(8-3x)} - \frac{8}{7(2x-3)}

Step-by-step solution

4 steps
  1. Factorize the denominator.

    The denominator is 25x−24−6x225x - 24 - 6x^2. Rearrange it into standard quadratic form:

    −6x2+25x−24-6x^2 + 25x - 24

    Factor out −1-1:

    −(6x2−25x+24)-(6x^2 - 25x + 24)

    Now, factorize the quadratic expression 6x2−25x+246x^2 - 25x + 24. We look for two numbers that multiply to 6×24=1446 \times 24 = 144 and add up to −25-25. These numbers are −9-9 and −16-16.

    6x2−9x−16x+246x^2 - 9x - 16x + 24

    Factor by grouping:

    3x(2x−3)−8(2x−3)3x(2x - 3) - 8(2x - 3) (3x−8)(2x−3)(3x - 8)(2x - 3)

    So, the denominator is −(3x−8)(2x−3)-(3x - 8)(2x - 3), which can also be written as (8−3x)(2x−3)(8 - 3x)(2x - 3).
    The expression becomes:

    2x−7(8−3x)(2x−3)\frac{2x-7}{(8-3x)(2x-3)}
  2. Set up the partial fraction decomposition.

    We express the fraction as a sum of two simpler fractions:

    2x−7(8−3x)(2x−3)=A8−3x+B2x−3\frac{2x-7}{(8-3x)(2x-3)} = \frac{A}{8-3x} + \frac{B}{2x-3}

    Multiply both sides by (8−3x)(2x−3)(8-3x)(2x-3) to clear the denominators:

    2x−7=A(2x−3)+B(8−3x)2x-7 = A(2x-3) + B(8-3x)
  3. Solve for the constants A and B.

    To find A, set 2x−3=02x-3 = 0, which means x=32x = \frac{3}{2}:

    2(32)−7=A(2(32)−3)+B(8−3(32))2\left(\frac{3}{2}\right) - 7 = A\left(2\left(\frac{3}{2}\right) - 3\right) + B\left(8 - 3\left(\frac{3}{2}\right)\right) 3−7=A(3−3)+B(8−92)3 - 7 = A(3 - 3) + B\left(8 - \frac{9}{2}\right) −4=A(0)+B(162−92)-4 = A(0) + B\left(\frac{16}{2} - \frac{9}{2}\right) −4=B(72)-4 = B\left(\frac{7}{2}\right) B=−4×27=−87B = -4 \times \frac{2}{7} = -\frac{8}{7}

    To find B, set 8−3x=08-3x = 0, which means 3x=83x = 8, so x=83x = \frac{8}{3}:

    2(83)−7=A(2(83)−3)+B(8−3(83))2\left(\frac{8}{3}\right) - 7 = A\left(2\left(\frac{8}{3}\right) - 3\right) + B\left(8 - 3\left(\frac{8}{3}\right)\right) 163−7=A(163−93)+B(8−8)\frac{16}{3} - 7 = A\left(\frac{16}{3} - \frac{9}{3}\right) + B(8 - 8) 163−213=A(73)+B(0)\frac{16}{3} - \frac{21}{3} = A\left(\frac{7}{3}\right) + B(0) −53=A(73)-\frac{5}{3} = A\left(\frac{7}{3}\right) A=−53×37=−57A = -\frac{5}{3} \times \frac{3}{7} = -\frac{5}{7}
  4. Write the final partial fraction expression.

    Substitute the values of A and B back into the partial fraction form:

    2x−725x−24−6x2=−578−3x+−872x−3\frac{2x-7}{25x-24-6x^2} = \frac{-\frac{5}{7}}{8-3x} + \frac{-\frac{8}{7}}{2x-3}

    This can be written as:

    −57(8−3x)−87(2x−3)-\frac{5}{7(8-3x)} - \frac{8}{7(2x-3)}
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