［log(a)(x)表示a为底x的对数］log(a)(x)＋log(a)(y)=log(a)(xy);log(a)(x)－log(a)(y)=log(a)(x/y)log(a^m)(x^n)=(n/m)log(a)(x)换底公式log(a)(x)=log(b)(x)/log(b)(a)=lg(x)/lg(a)=ln(x)/ln(a)
