一个数列前n项和为Sn=1-2+3-4----+(-1）的n+1次方*n,则S17+S33+S50=?

n为偶数,Sn=(1-2)+(3-4)+……+(n-1)×(-1)^n+n×(-1)^(n+1)=-n/2n为奇数,Sn=1+(-2+3)+(-4+5)+……+(n-1)×(-1)^n+n×(-1)^(n+1)=(n+1)/2S17=(17+1)/2=9S33=(33+1)/2=17S50=-50/2=-25S17+S33+S50=1