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