求数列通项1.已知数列{an}满足:a(n+1)方=an方+4且a1=1,an>0,求an2.在数列{an}中,a1=2
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求数列通项
1.已知数列{an}满足:a(n+1)方=an方+4且a1=1,an>0,求an
2.在数列{an}中,a1=2,a(n+1)=an+3n+2,求an
3.已知a1=1,a(n+1)-an=2的n次方-n,求an
注:(n+1)是a的角标
1.已知数列{an}满足:a(n+1)方=an方+4且a1=1,an>0,求an
2.在数列{an}中,a1=2,a(n+1)=an+3n+2,求an
3.已知a1=1,a(n+1)-an=2的n次方-n,求an
注:(n+1)是a的角标
![求数列通项1.已知数列{an}满足:a(n+1)方=an方+4且a1=1,an>0,求an2.在数列{an}中,a1=2](/uploads/image/z/7841620-28-0.jpg?t=%E6%B1%82%E6%95%B0%E5%88%97%E9%80%9A%E9%A1%B91.%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%7Ban%7D%E6%BB%A1%E8%B6%B3%EF%BC%9Aa%EF%BC%88n%2B1%EF%BC%89%E6%96%B9%3Dan%E6%96%B9%2B4%E4%B8%94a1%3D1%2Can%3E0%2C%E6%B1%82an2.%E5%9C%A8%E6%95%B0%E5%88%97%7Ban%7D%E4%B8%AD%2Ca1%3D2)
1.a(n+1)^2=an^2+4,令bn=an^2,b(n+1)=bn+4,b1=a1^2=1
bn是一个等差数列,其通项bn=4(n-1)+1=4n-3
因an>0,an=√(4n-3)
2.在数列{an}中,a1=2,a(n+1)=an+3n+2,求an
an=a(n-1)+3(n-1)+2=a(n-2)+3(n-2)+2+3(n-1)+2=a(n-3)+3(n-3)+2+3(n-2)+2+3(n-1)+2=a1+3[1+2+...+(n-1)]+(n-1)*2
=2+3n(n-1)/2+2n-2=3n(n-1)/2+2n
=n(3n+1)/2
3.已知a1=1,a(n+1)-an=2^n-n,求an
an-a(n-1)=2^(n-1)-(n-1)
a(n-1)-a(n-2)=2^(n-2)-(n-2)
...
a2-a1=2^1-1
以上各式相加:
an-a1=2^1+...+2^(n-2)+2^(n-1)-[1+...+(n-2)+(n-1)]
=2^n-2-n(n-1)/2
an=a1+2^n-2-n(n-1)/2=2^n-n(n-1)/2-1
bn是一个等差数列,其通项bn=4(n-1)+1=4n-3
因an>0,an=√(4n-3)
2.在数列{an}中,a1=2,a(n+1)=an+3n+2,求an
an=a(n-1)+3(n-1)+2=a(n-2)+3(n-2)+2+3(n-1)+2=a(n-3)+3(n-3)+2+3(n-2)+2+3(n-1)+2=a1+3[1+2+...+(n-1)]+(n-1)*2
=2+3n(n-1)/2+2n-2=3n(n-1)/2+2n
=n(3n+1)/2
3.已知a1=1,a(n+1)-an=2^n-n,求an
an-a(n-1)=2^(n-1)-(n-1)
a(n-1)-a(n-2)=2^(n-2)-(n-2)
...
a2-a1=2^1-1
以上各式相加:
an-a1=2^1+...+2^(n-2)+2^(n-1)-[1+...+(n-2)+(n-1)]
=2^n-2-n(n-1)/2
an=a1+2^n-2-n(n-1)/2=2^n-n(n-1)/2-1
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