练习:写出典型方程,并求 出自由项。 81X1+812X2+13X3+△C=-b 21X1+2X2+O23X3+△2C=-a 621X1+2X,+02X2+△ △C=0△2C=0△3c=0 61X1+O12X2+13X3+△c=0 621X1+62X,+62X2+△c=0 X 31X1+632X2+63X3+△3c=0 X ×b+(-D) X,=1练习:写出典型方程,并求 出自由项。      + + +  = − + + +  = − + + +  = −           C C C X X X X X X a X X X b 3 1 1 3 2 2 3 3 3 3 2 1 1 2 2 2 2 3 3 2 1 1 1 1 2 2 1 3 3 1 1C=0 2C=0 3C=0 X1 X3 X2 X1 X3 X2      + + +  = + + +  = + + +  = 0 0 0 31 1 32 2 33 3 3 21 1 22 2 23 3 2 11 1 12 2 13 3 1 C C C X X X X X X X X X          X2 =1 0 0 1 X1 =1 1 0 l 0 1 0 X3 =1 1     = −  = − = −  = −  + −  C C C a l b b l 3 2 1 [1 ( ) ]