数列{an}满足a1=1,a2=2,an+2=2an+1-an+2

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数列{an}满足a1=1,a2=2,an+2=2an+1-an+2
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数列{an}满足a1=1,a2=2,an+2=2an+1-an+2
数列{an}满足a1=1,a2=2,an+2=2an+1-an+2

数列{an}满足a1=1,a2=2,an+2=2an+1-an+2
(Ⅰ)由an+2=2an+1-an+2得,
an+2-an+1=an+1-an+2,
由bn=an+1-an得,bn+1=bn+2,
即bn+1-bn=2,
又b1=a2-a1=1,
所以{bn}是首项为1,公差为2的等差数列.
(Ⅱ)由(Ⅰ)得,bn=1+2(n-1)=2n-1,
由bn=an+1-an得,an+1-an=2n-1,
则a2-a1=1,a3-a2=3,a4-a3=5,…,an-an-1=2(n-1)-1,
所以,an-a1=1+3+5+…+2(n-1)-1
=
(n−1)(1+2n−3)
2
=(n-1)2,
又a1=1,
所以{an}的通项公式an=(n-1)2+1=n2-2n+2.