4x+9y=12.(1)3y-2z=1.(2)7x+5z=4.(3)(1)-(2)*3得,4x+6z=9.(4)(3)*6-(4)*5得,22x=-21x=-21/22将x=-21/22代入(1)得,4*(-21/22)+9y=129y=12-4*(-21/22)=(12*22+4*21)/22y=(12*22+4*21)/(22*9)=384/22*9=58/33将x=-21/22...