求图中四阶行列式答:D=-a*|(a,0,b)(0,d,0)(c,0,d)|+b*|(a,0,b)(0,c,0)(c,0,d)| 【按r1展开】=-ad*|(a,b)(c,d)|+bc*|(a,b)(c,d)| 【都按r2展开】=-ad(ad-bc)+bc*(ad-bc)=-(ad)^2+abcd+abcd-(bc)^2 =-(ad-bc)^2 ...
求图中四阶行列式答:D=-|(a,0,0,b)(0,a,b,0)(0,c,d,0)(c,0,0,d)| 【交换r1、r2】=-|(a,0,0,b)(0,a,b,0)(0,0,d-bc/a,0)(0,0,0,d-bc/a)| 【r3-r2*(c/a)、r4-r1*(c/a)】=-a^2(d-bc/a)^2 【上三角】=-(ad-bc)^2 ...