1. Rút gọn
a, $\sqrt{\sqrt{log_{b}^{4}a+log_{a}^{4}b+2}-2}$ với $1< a< b$.
b, $\left ( log_{a} b+log_{b}a+2\right )\left ( log_{a}b-log_{ab}b \right )log_{b}a$.
c, $log_{a+b}c+log_{a-b}c-2log_{a+b}clog_{a-b}c$ với $\left ( b^{2} +c^{2}=a^{2}\right )$.
d, $\frac{1- log_{a}^{3}b}{(log_{a}b+log_{b}a+1)log_{a}\frac{a}{b}}$.
