a1=2,
3a(n+1)+an-7=0 (1)
设a(n+1)+k=-1/3(an+k)
a(n+1)+k=-1/3an-k/3
3a(n+1)=-an-k-3k
-4k=7
k=-7/4
a1-7/4
=2-7/4
=1/4
{an-7/4}是以1/4首项,-1/3的等比数列
an-7/4=1/4*(-1/3)^(n-1)
an=1/4*(-1/3)^(n-1)+7/4
a1=2,
3a(n+1)+an-7=0 (1)
设a(n+1)+k=-1/3(an+k)
a(n+1)+k=-1/3an-k/3
3a(n+1)=-an-k-3k
-4k=7
k=-7/4
a1-7/4
=2-7/4
=1/4
{an-7/4}是以1/4首项,-1/3的等比数列
an-7/4=1/4*(-1/3)^(n-1)
an=1/4*(-1/3)^(n-1)+7/4