若数列{an}是等差数列,a1=50,d=-2,Sn=0,则n的值是

若数列{an}是等差数列,a1=50,d=-2,Sn=0,则n的值是
若数列{an}是等差数列,a1=50,d=-2,Sn=0,则n的值是

若数列{an}是等差数列,a1=50,d=-2,Sn=0,则n的值是
an=50-2(n-1)=52-2n
所以Sn=(a1+an)*n/2=(102-2n)*n/2=0
n不等于0
所以102-2n=0
n=51