Expand \((1 + 2x)^{-3}\) in ascending powers of \(x\), up to and including the term in \(x^2\), simplifying the coefficients.
Solution
To expand \((1 + 2x)^{-3}\), we use the binomial series expansion for negative exponents:
\((1 + u)^{n} = 1 + nu + \frac{n(n-1)}{2!}u^2 + \cdots\)
Here, \(u = 2x\) and \(n = -3\).
First term: \(1\).
Second term: \(-3(2x) = -6x\).
Third term: \(\frac{-3(-4)}{2}(2x)^2 = \frac{12}{2}(4x^2) = 24x^2\).
Thus, the expansion up to \(x^2\) is \(1 - 6x + 24x^2\).
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