log1/4 x=lgx/lg(1/4)=lgx/lg2^(-2)=lgx/(-2lg2)=(-1/2)log2(x)
所以log2(x)>(-1/2)log2(x)+3
(3/2)log2(x)>3
log2(x)>2=log2(4)
底数2>1
所以log2(x)是增函数
所以x>4