等差数列{an},{bn}的前n项和分别为Sn,Tn,Sn/Tn=2n/3n+1则a3/b5

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等差数列{an},{bn}的前n项和分别为Sn,Tn,Sn/Tn=2n/3n+1则a3/b5
是a3/b5不是其他

2n/3n+1?
2n/(3n+1)?
2n/(3n+1):,n=1,a1/b1=1/2,b1=2a1
a2=a1+d,b2=b1+c=2a1+c,a2/b2=4/7=(a1+d)/(2a1+c),8a1+4c=7a1+7d,a1=7d-4c
a3=a1+2d,b3=b1+2c=2a1+2c,a3/b3=3/5=(a1+2d)/(2a1+2c),6a1+6c=5a1+10d,a1=10d-6c=7d-4c
3d=2c,c=3d/2,a1=7d-6d=d,b1=2d
a3=a1+2d=3d,b5=b1+4c=2d+6d=8d
a3/b5=3/8
再问： a2/b2��4/7��ܲ��ٰ�æ��һ��
再答： s2/t2=4/7=(2a1+d)/(2b1+c)=(2a1+d)/(4a1+c), 16a1+4c=14a1+7d,a1=7d/2-2c, a3=a1+2d,b3=b1+2c=2a1+2c, s3/t3=3/5=(3a1+3d)/(3b1+3c)=(3a1+3d)/(6a1+3c), 18a1+9c=15a1+15d,a1=5d-3c=7d/2-2c, c=3d/2,a1=7d/2-3d=d/2,b1=d, a3=a1+2d=5d/2,b5=b1+4c=d+6d=7d,a3/b5=5/14

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