1.
等式两边同除以√ana(n-1)
1/√an -1/√a(n-1)=1,为定值
1/√a1=1/√1=1,数列{1/√an}是以1为首项,1为公差的等差数列
1/√an=1+1×(n-1)=n
√an=1/n
an=1/n²
2.
a(n+1)+2an=2
a(n+1)=-2an+2
a(n+1)- 2/3=-2an+4/3 =-2(an -2/3)
[a(n+1)-2/3]/(an -2/3)=-2,为定值
a1-2/3=1-2/3=1/3,数列{an -2/3}是以1/3为首项,-2为公比的等比数列
an-2/3=(1/3)×2^(n-1)
an=[2+2^(n-1)]/3
3.
an=a(n-1)/[3a(n-1)+1]
1/an=[3a(n-1)+1]/a(n-1)=1/a(n-1) +3
1/an -1/a(n-1)=3,为定值
1/a1=1/1=1,数列{1/an}是以1为首项,3为公差的等差数列
1/an=1+3(n-1)=3n-2
an=1/(3n-2)
4.
an=3a(n-1)+2ⁿ
an=3a(n-1)+3×2ⁿ-2^(n+1)
an+2^(n+1)=3[a(n-1)+2ⁿ]
[an+2^(n+1)]/[a(n-1)+2ⁿ]=3,为定值
a1+2²=1+4=5,数列{an+2^(n+1)}是以5为首项,3为公比的等比数列
an+2^(n+1)=5×3^(n-1)
an=5×3^(n-1) -2^(n+1)