r4-r2
7 6 3 0
3 5 7 -1
5 4 3 0
2 1 -2 0
按第4列展开
= -1*(-1)^(2+4)*
7 6 3
5 4 3
2 1 -2
c1+c3,c3+2c2
10 6 15
8 4 11
0 1 0
按第3行展开
= 1*(-1)^(3+2)
10 15
8 11
= -10.