r3-2r1,r4-r1~1 1 2 2 10 2 1 5 -10 -2 -1 -5 10 0 -2 2 -2 r3+r2，交换r3 r4~1 1 2 2 10 2 1 5 -10 0 -2 2 -2 0 0 0 0 0只是求秩就不用再计算，显然矩阵的秩为3
