等差数列{an}中,a2=4,S6=42(1)求数列的通项公式an(2)设bn=2/[(n+1)an],Tn=b1+b2+……+bn,求T10.
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![等差数列{an}中,a2=4,S6=42(1)求数列的通项公式an(2)设bn=2/[(n+1)an],Tn=b1+b2+……+bn,求T10.](/uploads/image/z/10172242-10-2.jpg?t=%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%E4%B8%AD%2Ca2%3D4%2CS6%3D42%EF%BC%881%EF%BC%89%E6%B1%82%E6%95%B0%E5%88%97%E7%9A%84%E9%80%9A%E9%A1%B9%E5%85%AC%E5%BC%8Fan%282%29%E8%AE%BEbn%3D2%2F%5B%28n%2B1%29an%5D%2CTn%3Db1%2Bb2%2B%E2%80%A6%E2%80%A6%2Bbn%2C%E6%B1%82T10.)
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等差数列{an}中,a2=4,S6=42(1)求数列的通项公式an(2)设bn=2/[(n+1)an],Tn=b1+b2+……+bn,求T10.
等差数列{an}中,a2=4,S6=42(1)求数列的通项公式an
(2)设bn=2/[(n+1)an],Tn=b1+b2+……+bn,求T10.
等差数列{an}中,a2=4,S6=42(1)求数列的通项公式an(2)设bn=2/[(n+1)an],Tn=b1+b2+……+bn,求T10.
1.设公差为d a2=a1+d=4
s6=(a1+a6)*6/2=3*(2a1+5d)=42即 2a1+5d=14
所以d=2,a1=2
an=2+(n-1)*2=2n
2.bn=1/[(n+1)*n]=1/n-1/(n+1)
T10=1/1-1/11=10/11
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