4x+ 9y= 12,3y-2z=1,7x+5z=4的解

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=-21
x=-21/22
将x=-21/22代入(1)得,
4*(-21/22)+9y=12
9y=12-4*(-21/22)=(12*22+4*21)/22
y=(12*22+4*21)/(22*9)=384/22*9
=58/33
将x=-21/22代入(3)得,
7*(-21/22)+5z=4
5z=4+7*(21/22)=(4*22+7*21)/22
z=(4*22+7*21)/(22*5)=235/22*5
=47/22

(谁出的计算题,弄得这么繁杂的答案.)

X=69/7 Y=35/3 Z=13