(i) Express \(\frac{5x + 3}{(x + 1)^2(3x + 2)}\) in partial fractions.
(ii) Hence obtain the expansion of \(\frac{5x + 3}{(x + 1)^2(3x + 2)}\) in ascending powers of \(x\), up to and including the term in \(x^2\), simplifying the coefficients.
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Solution
(i) Express \(\frac{5x + 3}{(x + 1)^2(3x + 2)}\) in partial fractions as:
\(\frac{A}{x+1} + \frac{B}{(x+1)^2} + \frac{C}{3x+2}\)
Equating and solving for constants, we find \(A = 1, B = 2, C = -3\).
(ii) Expand each term:
\(\frac{1}{(x+1)^2} = (1 + x)^{-2} \approx 1 - 2x + 3x^2\)
\(\frac{1}{3x+2} = \frac{1}{2}(1 - \frac{3}{2}x + (\frac{3}{2}x)^2) \approx \frac{1}{2} - \frac{3}{4}x + \frac{9}{8}x^2\)
Combine and simplify:
\(\frac{5x + 3}{(x + 1)^2(3x + 2)} \approx \frac{3}{2} - \frac{11}{4}x + \frac{29}{8}x^2\)
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