第1章行列式 例题习题
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1.计算下列各行列式:(1)⎥⎥⎥⎥⎦⎥⎢⎢⎢⎢⎣⎢7110025********14; (2)⎥⎥⎥⎥⎦⎥⎢⎢⎢⎢⎣⎢-2605232112131412; (3)⎥⎥⎥⎦⎥⎢⎢⎢⎣⎢---ef cf bf de cd bd ae ac ab ; (4)⎥⎥⎥⎥⎦⎥⎢⎢⎢⎢⎣⎢---d c b a100110011001 解(1)711025102021421434327c c c c --01142310202110214---=34)1(143102211014+-⨯---=143102211014--321132c c c c ++1417172001099-=0(2)2605232112131412-24c c -2605032122130412-24r r -0412032122130412-14r r -0032122130412-=0(3)efcfbfde cd bdae ac ab---=ecbe c be c badf ---=111111111---adfbce =abcdef 4(4)dc b a1110011001---21ar r +dc b a ab 1110011010---+=12)1)(1(+--dc a ab11101--+ 23dc c +01111-+-+cd c ad a ab=23)1)(1(+--cdad ab +-+111=1++++ad cd ab abcd2.证明:(1)1112222b b a abab a+=3)(b a -; (2)bzay byax bx az by ax bx az bzay bxaz bz ay by ax +++++++++=yxzx z y z y x b a )(33+; (3)0)3()2()1()3()2()1()3()2()1()3()2()1(2222222222222222=++++++++++++d d d dc c c c b b b b a a a a;(4)444422221111dcbad c b a d c b a))()()()((d b c b d a c a b a -----=))((d c b a d c +++-⋅;(5)1221100000100001a x a a a a x x x n n n+-----n n n n a x a xa x ++++=--111 .证明 (1)0122222221312a b a b a ab a ab ac c c c ------=左边 ab ab ab a ab 22)1(22213-----=+21))((a b a a b a b +--=右边=-=3)(b a(2)bzay byax z by ax bx az y bxaz bz ay x a ++++++分开按第一列左边bzay by ax xby ax bx az z bx az bz ay yb +++++++ ++++++002y by ax zx bx az y zbz ay x a分别再分bzay yxby ax x z bx az z y b +++ zyx y x z x z yb y x zx z y z y x a33+分别再分右边=-+=233)1(y xzx z y zy xb yx zx z y z y x a(3) 2222222222222222)3()2()12()3()2()12()3()2()12()3()2()12(++++++++++++++++=d d d ddc c c c c b b b b b a a a a a左边9644129644129644129644122222141312++++++++++++---d d d d c c c c b b b b a a a ac c c c c c964496449644964422222++++++++d d ddc c c c b b b b a a a a分成二项按第二列964419644196441964412222+++++++++d d d c c c b b b a a a949494949464222224232423dd c cb b a ac c c c c c c c ----第二项第一项6416416416412222=+dddc c c b b b a a a(4) 444444422222220001adac ab aa d a c ab a a d ac a b a ---------=左边=)()()(222222222222222a d d a c c ab b adac ab a d ac a b ---------=)()()(111))()((222a d d a c c ab b a d ac a b ad a c a b ++++++---=⨯---))()((a d a c a b)()()()()(00122222a b b a d d a b b a c c a b b bd bc a b +-++-++--+=⨯-----))()()()((b d b c a d a c a b)()()()(112222b d a b bd db c a b bc c ++++++++=))()()()((d b c b d a c a b a -----))((d c b a d c +++-(5) 用数学归纳法证明.,1,2212122命题成立时当a x a x a x a x D n ++=+-==假设对于)1(-n 阶行列式命题成立,即 ,122111-----++++=n n n n n a x a x a x D:1列展开按第则n D1110010001)1(11----+=+-xx a xD D n n n n右边=+=-n n a xD 1所以,对于n 阶行列式命题成立.3.设n 阶行列式)det(ij a D =,把D 上下翻转、或逆时针旋转 90、或依 副对角线翻转,依次得nnnn a a a a D 11111=, 11112n nnn a a a a D= ,11113a a a a D n nnn=, 证明D D D D D n n =-==-32)1(21,)1(. 证明 )det(ij a D =nnn n n n nnn n a a a a a a a a a a D 2211111111111)1(--==∴=--=--nnn n nnn n a a a a a a a a 331122111121)1()1( nnn n n n a a a a111121)1()1()1(---=-- D D n n n n 2)1()1()2(21)1()1(--+-+++-=-=同理可证nnnn n n a a a a D11112)1(2)1(--=D Dn n Tn n 2)1(2)1()1()1(---=-=D D D D D n n n n n n n n =-=--=-=----)1(2)1(2)1(22)1(3)1()1()1()1(4.计算下列各行列式(阶行列式为k D k ):(1)aaD n 11 =,其中对角线上元素都是a ,未写出的元素都是0;(2)xaaa x a a a x D n=;(3) 1111)()1()()1(1111n a a a n a a a n a a aD n n n nnnn ------=---+;提示:利用范德蒙行列式的结果.(4) nnnnn d c d c b a b a D000011112=; (5)j i a a D ij ij n -==其中),det(;(6)nn a a a D +++=11111111121,021≠n a a a 其中.解(1) aa a a a D n 010000000000001000=按最后一行展开)1()1(10000000010000)1(-⨯-+-n n n aa a)1)(1(2)1(--⋅-+n n naaa(再按第一行展开)n n n nn a aa+-⋅-=--+)2)(2(1)1()1(2--=n n aa )1(22-=-a an(2)将第一行乘)1(-分别加到其余各行,得ax xa a x xa a x x a a a a x D n ------=00000再将各列都加到第一列上,得ax a x a x a a a an x D n ----+=000000)1()(])1([1a x a n x n --+=-(3)从第1+n 行开始,第1+n 行经过n 次相邻对换,换到第1行,第n 行经)1(-n 次对换换到第2行…,经2)1(1)1(+=++-+n n n n 次行交换,得nnnn n n n n n n a a a n a a ana a a D )()1()()1(1111)1(1112)1(1-------=---++此行列式为范德蒙德行列式∏≥>≥++++--+--=112)1(1)]1()1[()1(j i n n n n j a i a D∏∏≥>≥+++-++≥>≥++-∙-∙-=---=1121)1(2)1(112)1()][()1()1()]([)1(j i n n n n n j i n n n j i j i∏≥>≥+-=11)(j i n j i(4) nnnnn d c d c b a b a D 0011112=nn n n n nd d c d c b a b a a 0000011111111----展开按第一行00)1(1111111112c d c d c b a b a b nn n n n nn ----+-+2222---n n n n n n D c b D d a 都按最后一行展开由此得递推公式:222)(--=n n n n n n D c b d a D即 ∏=-=ni i i i in D c b d aD 222)(而 111111112c b d a d c b a D -==得 ∏=-=ni i i iin c b da D 12)((5)j i a ij -=432140123310122210113210)det(--------==n n n n n n n n a D ij n,3221r r r r --0432111111111111111111111 --------------n n n n,,141312c c c c c c +++1524232102221002210002100001---------------n n n n n =212)1()1(----n n n(6)nn a a a D +++=11111111121,,433221c c c c c c ---nnn n a a a a a a a a a a +-------10100010000100010001000011433221展开(由下往上)按最后一列))(1(121-+n n a a a a nn n a a a a a a a a a --------0000000000000000000000022433221n n n a a a a a a a a ----+--000000000000000001133221 ++nn n a a a a a a a a -------000000000000001143322n n n n n n a a a a a a a a a a a a 322321121))(1(++++=---)11)((121∑+==ni in a a a a5.用克莱姆法则解下列方程组:⎪⎪⎩⎪⎪⎨⎧=+++-=----=+-+=+++;01123,2532,242,5)1(4321432143214321x x x x x x x x x x x x x x x x ⎪⎪⎪⎩⎪⎪⎪⎨⎧=+=++=++=++=+.15,065,065,065,165)2(5454343232121x x x x x x x x x x x x x 解 (1)11213513241211111----=D 812735032101111------=145008130032101111---=1421420005410032101111-=---=112105132412211151------=D 11210513290501115----=1121023313090509151------=2331309050112109151------=1202300461000112109151-----=14200038100112109151----=142-=11235122412111512-----=D 811507312032701151-------=31390011230023101151-=28428401910023101151-=----= 42611135232422115113-=----=D14202132132212151114=-----=D1,3,2,144332211-========∴DD x DD x DD x DD x(2)5165100065100065100065=D 展开按最后一行610510********5-'D D D ''-'=65D D D ''-'''-''=6)65(5D D '''-''=3019D D ''''-'''=1146566551141965=⨯-⨯=(,11的余子式中为行列式a D D ',11的余子式中为a D D ''''类推D D ''''''',) 511651000651000650000611=D 展开按第一列651065100650006+'D46+'=D 460319+''''-'''=D 1507=51010651000650000601000152=D 展开按第二列51651006500061-651065000610005-36551651065⨯-=1145108065-=--=51100650000601000051001653=D 展开按第三列5165000610005165061000510065+61051065651650061+=703114619=⨯+= 5100601000051000651010654=D 展开按第四列6105100651006550610005100651--516516565--=395-= 11000051000651000651100655=D 展开按最后一列D '+15100651006512122111=+=665212;665395;665703;6651145;665150744321=-==-==∴x x x x x .6.齐次线性方程组取何值时问,,μλ⎪⎩⎪⎨⎧=++=++=++0200321321321x x x x x x x x x μμλ有非零解? 解 μλμμμλ-==12111113D ,齐次线性方程组有非零解,则03=D 即 0=-μλμ 得 10==λμ或不难验证,当,10时或==λμ该齐次线性方程组确有非零解.。