an=4a(n-1)+1
an+1/3 =4[a(n-1)+1/3]
{an+1/3}是以7/3为首相的等比数列
an+1/3=4^(n-1)(7/3)
an=4^(n-1)(7/3)-1/3{an+1/3}是以7/3为首相的等比数列怎么来的你额没看到an+1/3=4[a(n-1)+1/3]an+1/3是等比数列首相就是a1+1/3=7/3