Expand \((2 + x^2)^{-2}\) in ascending powers of \(x\), up to and including the term in \(x^4\), simplifying the coefficients.
Solution
To expand \((2 + x^2)^{-2}\), we use the binomial series expansion for negative exponents:
\((1 + u)^{-n} = 1 - nu + \frac{n(n+1)}{2!}u^2 - \frac{n(n+1)(n+2)}{3!}u^3 + \cdots\)
Here, \(u = \frac{x^2}{2}\) and \(n = 2\).
First term: \(\frac{1}{4}\).
Second term: \(-2 \times \frac{x^2}{2} = -x^2\).
Third term: \(\frac{2 \times 3}{2} \left(\frac{x^2}{2}\right)^2 = \frac{3}{16}x^4\).
Thus, the expansion up to \(x^4\) is \(\frac{1}{4} - \frac{1}{4}x^2 + \frac{3}{16}x^4\).
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