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高中文科数学,打字不怎么看得懂可以在纸上拍下来,求详细过程,希望公式也写一下!!!
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(1)an=Sn-S(n-1)=1/2[3n²-n-(3(n-1)²-(n-1))]=3n-2
n=1时,S1=a1=1,合理,所以an=3n-2
(2)a1=1,an=3n-2,am=3m-2
若a1,an,am成等比数列则有:(an)²=a1*am
(3n-2)²=3m-2
m=1/3[(3n-2)²+2]=1/3(9n²-12n+6)=3n²-4n+2
即对应任意的n>1,都有m=3n²-4n+2与之对应使得a1,an,am成等比数列
n=1时,S1=a1=1,合理,所以an=3n-2
(2)a1=1,an=3n-2,am=3m-2
若a1,an,am成等比数列则有:(an)²=a1*am
(3n-2)²=3m-2
m=1/3[(3n-2)²+2]=1/3(9n²-12n+6)=3n²-4n+2
即对应任意的n>1,都有m=3n²-4n+2与之对应使得a1,an,am成等比数列
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