log2x+2log4x+log8x=7
因为2log4x=2*1/2 log2x= log2x
log8x=1/3 log2x
所以log2x+2log4x+log8x= log2x+ log2x+1/3 log2x=7/3 log2x=7
即log2x=3
故x=8