Find the coefficient of x in the expansion of \(\left( x + \frac{2}{x^2} \right)^7\).
Solution
To find the coefficient of \(x\) in the expansion of \(\left( x + \frac{2}{x^2} \right)^7\), we use the binomial theorem:
\(\left( x + \frac{2}{x^2} \right)^7 = \sum_{k=0}^{7} \binom{7}{k} x^{7-k} \left( \frac{2}{x^2} \right)^k\)
We need the term where the power of \(x\) is 1:
\(7-k - 2k = 1\)
Solving for \(k\):
\(7 - 3k = 1\)
\(3k = 6\)
\(k = 2\)
Substitute \(k = 2\) into the binomial term:
\(\binom{7}{2} x^{7-2} \left( \frac{2}{x^2} \right)^2 = \binom{7}{2} x^5 \left( \frac{4}{x^4} \right)\)
\(= \binom{7}{2} \cdot 4 \cdot x = 21 \cdot 4 \cdot x = 84x\)
Thus, the coefficient of \(x\) is 84.
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