运算法则题目1

解答：
$令 4^{a} = 6^{b} = 9^{c} = k, 则 a = \log_{4} k, b = \log_{6} k, c = \log_{9} k$

$\frac{1}{a} - \frac{2}{b} + \frac{1}{c} = \log_{k} 4 - 2 \log_{k} 6 + \log_{k} 9 = \log_{k} 1 = 0$