abc成等差,所以2b=a+c
acb成等比,所以c^2=ab
(2b-a)^2=ab
a^2-5ab+4b^2=0
(a-4b)(a-b)=0
a=4b或a=b
c=-2b或c=b
因此a:b:c=4:1:-2或a:b:c=1:1:1