设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?

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设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?
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设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?
设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?

设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?
Sn=n/2*(a1+an)=n/2*(a5+an-4)=136 n=2*136/32 带进正确的值求出

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