S(n+2)=∑x(n+2)=x(n+1)-x(n)+x(n)-x(n-1)+...+x2-x1+x2+x1=x(n+1)-x1+x1+x2=x(n+1)+x2取n=98S100=x99+x2x99满足6m+9所以是-8即S100=-8+3=-5
