解方程组：x+2y=3(1) y+2z=4 (2) z+2x=5 (3)

y+2z=4
y=4-2z
代入(1)x+8-4z=3 (4)
z+2x=5 (3)
(4)+(3)×4
x+8-4z+4z+8x=3+20
9x=15
所以x=5/3
z=5-2x=5/3
y=4-2z=2/3x:y:z=2:3:9x+y+z=70令a=x/2=y/3=z/9 x=2a,y=3a,z=9a 2a+3a+9a=70 14a=70 a=5 所以x=10,y=15,z=45