对数有意义,ab>0 a,b,ab成等比数列,设公比为q (q≠0) a=ab/q>0,因此b>0 a>0 b>0 a,b,a+b成等差数列,则2b=a+a+b b=2a a,b,ab成等比数列,则 b=a(ab)=ab b=a 2a=a a(a-2)=0 a=0(舍去)或a=2 b=2a=4 ab=8 0