不等式log0.5x-81logx0.5+7>0的解集为:( )不等式log0.5x-81*logx0.5+7>0的解集为:( )A (1,2)U(0,1/2) B(2,24)U(1,1/2) C (1,28)U(0,1/2) D [1,2]U(0,1/2)

问题描述:

不等式log0.5x-81logx0.5+7>0的解集为:( )
不等式log0.5x-81*logx0.5+7>0的解集为:( )
A (1,2)U(0,1/2) B(2,24)U(1,1/2) C (1,28)U(0,1/2) D [1,2]U(0,1/2)

81错了
即lgx/lg0.5-8lg0.5/lgx+7>0
令a=lgx/lg0.5
a-8/a+7>0
若a>0
则a²+7a-8>0
所以a>1
lgx/lg0.5>1
lgx0若a则a²+7a-8所以-8-800所以0