若 Sn=75/4(5^n-1) tn=?答案是75(5^n-1).
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若Sn=75/4(5^n-1)tn=?答案是75(5^n-1).若Sn=75/4(5^n-1)tn=?答案是75(5^n-1).若Sn=75/4(5^n-1)tn=?答案是75(5^n-1).如果是这
若 Sn=75/4(5^n-1) tn=?答案是75(5^n-1).
若 Sn=75/4(5^n-1) tn=?答案是75(5^n-1).
若 Sn=75/4(5^n-1) tn=?答案是75(5^n-1).
如果是这个答案,就说明(5^n-1)是分子
tn=Sn-S(n-1)=75*0.25*(5^n-1)-75*0.25*(5^(n-1)-1)
=75*0.25*(5^n-5^(n-1))=75*0.25*(5*5^(n-1)-5^(n-1))
=75*0.25*4*5^(n-1)
=75*(5^(n-1))
写错了吧?
是75(5^(n-1))吧.
tn = Sn - S(n-1)
= 75/4(5^n-1) - 75/4(5^(n-1)-1)
= 75/4(5^n - 5^(n-1))
= 75/4 * 5^(n-1)*4
= 75*(5^(n-1))
若 Sn=75/4(5^n-1) tn=?答案是75(5^n-1).
·求tn=?Sn=75/4(5^n-1)
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