数列{an}中①Sn=π(2n²+n)/12 ②Sn=2/3(3n-1) 求an
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数列{an}中①Sn=π(2n²+n)/12 ②Sn=2/3(3n-1) 求an
数列{an}中①Sn=π(2n²+n)/12 ②Sn=2/3(3n-1) 求an
数列{an}中①Sn=π(2n²+n)/12 ②Sn=2/3(3n-1) 求an
(1)
Sn=π(2n^2+n)/12 (1)
S(n-1)=π(2(n-1)^2+(n-1))/12 (2)
(1)-(2)
an=(π/12)(4n-1)
(2)
Sn=(2/3)(3n-1) (1)
S(n-1)=(2/3)(3(n-1)-1) (2)
(1)-(2)
an =2