3(k+1)=1/3(k-1)+2(k+10-1/2(k-1)

3(k+1)=1/3(k-1)+2(k+1）-1/2(k-1)
3（k+1）-2（k+1）=2/6(k-1)-3/6(k-1)
k+1=-1/6（k-1）
k+1=1/6-1/6k
7/6k=-5/6
k=-5/7
ok了
还帮你带进去验证了下,是正确的.