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写出下列数列的前5项.1.a1=1,a2=2,an+2=2an+1+an2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
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写出下列数列的前5项.
1.a1=1,a2=2,an+2=2an+1+an
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
1.a1=1,a2=2,an+2=2an+1+an
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
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答案和解析
1.a1=1,a2=2,an+2=2an+1+an
a1=1,a2=2,a3=2a2+a1=5,a4=2a3+a2=12,a5=2a4+a3=29
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
a1=-1,a2=-2,
a3=1/(a2)+1/a1=1/(-2)+1/(-1)=-3/2
a4=1/(a3)+1/a2=1/(-3/2)+1/(-2)=-7/6
a5=1/(a4)+1/a3=1/(-7/6)+1/(-3/2)=-32/21
a1=1,a2=2,a3=2a2+a1=5,a4=2a3+a2=12,a5=2a4+a3=29
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
a1=-1,a2=-2,
a3=1/(a2)+1/a1=1/(-2)+1/(-1)=-3/2
a4=1/(a3)+1/a2=1/(-3/2)+1/(-2)=-7/6
a5=1/(a4)+1/a3=1/(-7/6)+1/(-3/2)=-32/21
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