r2-r1,r4-r11 2 0 10 1 5 -10 1 5 60 0 3 3r3-r21 2 0 10 1 5 -10 0 0 70 0 3 3r3<->r4 (行列式变符号)1 2 0 10 1 5 -10 0 3 30 0 0 7= -21.