y=(x²-1+12)/(x+1)
=(x²-1)/(x+1)+12/(x+1)
=x-1+12/(x+1)是整数
则12能被x+1整除
所以x+1=1,-1,2,-2,3,-3,4,-4,6,-6,12,-12
x有12个值
这12个值互为相反数,所以和是0
即 12(x+1)=0
12x+12=0
所以和是-12