题目

若(logax)=x(a＞0,a≠1)，则x的值等于(    )A.1或a                   B.1或aa                C.aa               D.a 答案：解析：利用换元法解方程.∵(logax)=x，∴loga［(logax)］=logax.∴(logax)［loga(logax)］=logax.设logax=t，则有tlogat=t，即t(logat-1)=0.∴t=0或logat=1.∴t=0或t=a.∴logax=0或logax=a.∴x=1或x=aa.经检验x=1不合题意舍去，故x=aa.故选C.答案：C17、Venus has a dense atmosphere, _____ we know very little.                   A. its composition                              B. whose composition C. about which composition                D. about whose composition