(i) Find the first 3 terms in the expansion, in ascending powers of \(x\), of \((1 - 2x^2)^8\).
(ii) Find the coefficient of \(x^4\) in the expansion of \((2 - x^2)(1 - 2x^2)^8\).
Solution
(i) Use the binomial expansion formula: \((1 + ax)^n = 1 + n(ax) + \frac{n(n-1)}{2!}(ax)^2 + \ldots\)
For \((1 - 2x^2)^8\), the first three terms are:
\(1 + 8(-2x^2) + \binom{8}{2}(-2x^2)^2\)
\(= 1 - 16x^2 + 112x^4\)
(ii) Expand \((2 - x^2)(1 - 16x^2 + 112x^4)\).
The coefficient of \(x^4\) is found by considering:
\((2 \times 112) - (-16) = 240\)
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