Expand \((2 + 3x)^{-2}\) in ascending powers of \(x\), up to and including the term in \(x^2\), simplifying the coefficients.
Solution
To expand \((2 + 3x)^{-2}\), we can use the binomial series expansion for negative exponents:
\((1 + u)^{-n} = 1 - nu + \frac{n(n+1)}{2!}u^2 - \cdots\)
Let \(u = \frac{3}{2}x\) and \(n = 2\), so \((2 + 3x)^{-2} = \left(2(1 + \frac{3}{2}x)\right)^{-2} = \frac{1}{4}(1 + \frac{3}{2}x)^{-2}\).
Now expand \((1 + \frac{3}{2}x)^{-2}\):
\(1 - 2\left(\frac{3}{2}x\right) + \frac{2 \cdot 3}{2!}\left(\frac{3}{2}x\right)^2\)
\(= 1 - 3x + \frac{9}{2}x^2\)
Multiply by \(\frac{1}{4}\):
\(\frac{1}{4}(1 - 3x + \frac{9}{2}x^2) = \frac{1}{4} - \frac{3}{4}x + \frac{27}{16}x^2\)
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