问题476: (3*a/(a**2 - 1) - 1/(a - 1)) / ((2*a - 1)/(a + 1))

$$ \begin{aligned} & \frac{\frac{3 a}{a^2-1}-\frac{1}{a-1}}{\frac{2 a-1}{a+1}} \\ = & \frac{3 a-(a+1)}{(2 a-1)(a-1)} \\ = & \frac{2 a-1}{(2 a-1)(a-1)} \\ = & \frac{1}{a-1} \end{aligned} $$

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