15题,15题,
15题,a(n+1)=2an+3a(n+1)+3=2an+6=2(an+3)(a(n+1)+3)/(an+3)=2∴an+3是等比数列a1+3=1+3=4∴an+3=4*2^(n-1)=2^2*2^(n-1)=2^(n+1)an=2^(n+1)-3(2)稍等