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    Laurent series of $\frac{1}{z(z-1)}$ on $\abs z<1$ and on $\abs z>1$

    E-BUVLS

    Area
    Complex Analysis
    Topics
    Laurent Series, Poles
    Status
    draft

    Expand \(f(z) = {1\over z(z-1)}\) in both

    • \(\abs{z} < 1\)
    • \(\abs{z} > 1\)
    Solution

    \[ {1\over z(z-1)} = -{1\over z}{1 \over 1-z} = -{1\over z}\sum z^k .\] and \[ {1\over z(z-1)} = {1\over z^2(1 - {1\over z})} = {1\over z^2} \sum \qty{1\over z}^k .\]