-1 4 3 1
2 -2 -1 3
1 2 3 1
3 0 2 4
r1+2r2,r3+r2
3 0 1 7
2 -2 -1 3
3 0 2 4
3 0 2 4
= 0 (两行相等则行列式等于0)
a b a+b
b a+b a
a+b a b
c1+c2+c3
2a+2b b a+b
2a+2b a+b a
2a+2b a b
r2-r1,r3-r1
2a+2b b a+b
0 a -b
0 a-b -a
= (2a+2b)(-a^2-(b^2-ab))
= -2(a+b)(a^2-ab+b^2)
= -2(a^3+b^3)