设数列{an}前n项和Sn,且a1=1,Sn=4a(n-1)+2(n≥2)
(1)设bn=a(n+1)-2an,求证{bn}是等比数列
(2)设cn=an/2^n,求证{cn}是等差数列
注:n+1,n-1为下标.