设Sn为等比数列an的前n项和,且a2=4,Sn=2(1)求an(2)设等差数列bn的前n项和为Tn,若b2=a1,b5=a2,求bn和T3
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![设Sn为等比数列an的前n项和,且a2=4,Sn=2(1)求an(2)设等差数列bn的前n项和为Tn,若b2=a1,b5=a2,求bn和T3](/uploads/image/z/14334846-6-6.jpg?t=%E8%AE%BESn%E4%B8%BA%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97an%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%2C%E4%B8%94a2%3D4%2CSn%3D2%281%29%E6%B1%82an%EF%BC%882%EF%BC%89%E8%AE%BE%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97bn%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BATn%2C%E8%8B%A5b2%3Da1%2Cb5%3Da2%2C%E6%B1%82bn%E5%92%8CT3)
设Sn为等比数列an的前n项和,且a2=4,Sn=2(1)求an(2)设等差数列bn的前n项和为Tn,若b2=a1,b5=a2,求bn和T3
设Sn为等比数列an的前n项和,且a2=4,Sn=2
(1)求an(2)设等差数列bn的前n项和为Tn,若b2=a1,b5=a2,求bn和T3
设Sn为等比数列an的前n项和,且a2=4,Sn=2(1)求an(2)设等差数列bn的前n项和为Tn,若b2=a1,b5=a2,求bn和T3
s2=a1+a2=2 a2=4
a1=-2 a2/a1=q=-2
an=(-2)*(-2)^(n-1)
b5-b2=3d=a2-a1=6 d=2
b2=4
b1=2
bn=a1+(n-1)*d=2n-4
T3=b1+b2+b3=12
sn几等于2都不说怎么算anS2=2(1)a2=a1q=4 a1=s2-a2=-2 a1=-2 q=-2 an=(-2)^n
(2)b2=a1=-2 b5=a2=4 d=2 b1=-2 bn=-4+(n-1)*2=2n-6 T3=a1+a2+a3=-6(1)a2=a1q=4 a1=s2-a2=-2 a1=-2 q=-2 an=(-2)^n
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sn几等于2都不说怎么算an
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