(lgc/a)^2=4lga/b.lgb/c,可以知道a,b,c都非0(lga/c)²=4lg(a/b).lg(b/c)[lg(a/b)+lg(b/c)]²=4lg(a/b).lg(b/c)∴ [lg(a/b)-lg(b/c)]²=0∴ lg(a/b)=lg(b/c)∴ a/b=b/c∴ a,b,c成等比数列.选A...

第二部怎么弄的啊

• (lga/c)²=4lg(a/b).lg(b/c)
  

第二步就是照抄啊然后lg(a/c)=lg(a/b)*(b/c)=lg(a/b)+lg(b/c)