y1=6^0.7 y2=0.7^6 y3=log0.7 1
6^0.7＞6^0＞1
0＜0.7^6＜0.7^0＜1
log0.7 1=0
所以y1＞y2＞y3
即6^0.7＞0.7^6＞log0.7 1