a1=3,an=2an-1+3 证{an+3}等比,并求an

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a1=3,an=2an-1+3 证{an+3}等比,并求an
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a1=3,an=2an-1+3 证{an+3}等比,并求an
a1=3,an=2an-1+3 证{an+3}等比,并求an

a1=3,an=2an-1+3 证{an+3}等比,并求an
(1)an=2a+3,
∴an+3=2[a+3],
∴数列{an+3}是等比数列.
(2)an+3=(a1+3)*2^(n-1),
an=(a1+3)*2^(n-1)-3=(6)*2^(n-1)-3.

an=2a(n-1)+3
an+3=2a(n-1)+6
an+3=2[2a(n-1)+3]
bn=an+3
bn=2b(n-1)
bn为等比数列
则an+3为等比数列
求出bn后an=bn-3即可算出an