例4.证明：a..ak O...au:11ak...ak O...0Cu...Cik bi....b...akiCr....Crk br....br.区$2.6行列式按一行（列）展开§2.6 行列式按一行（列）展开 例4.证明： 11 1 11 1 11 1 1 11 1 11 1 1 1 1 1 0 0 0 0 k k r k kk k r k kk r rr r rk r rr a a a a b b a a c c b b a a b b c c b b =