设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6,则n=

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设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6,则n=设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6

设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6,则n=
设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6,则n=

设Sn是等差数列{an}的前n项和好,已知S6=36,Sn=324,S(n-6)=144,n>6,则n=
Sn是等差数列
S6=a1*6+6(6-1)/2*d=36,则2a1+5d=12.&
最后六项的和S=an*6-6(6-1)/2*d=6an-15d
S(n-6)=Sn-S=324-(6an-15d)=144,则2an-5d=60.@
&+@:a1+an=36
Sn=(a1+an)/2*n
n=18

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