x :y = 3 :4
4x = 3y
x = 3y/4__i
y :z = 2 :5
5y = 2z
z = 5y/2__ii
2x + y - z = 66__iii
把 i 和 ii 放入 iii 里,
2(3y/4) + y - (5y/2) = 66
3y/2 + y - 5y/2 = 66
3y + y - 5y = 132
y = -132
当 y = -132,从 i,
x = 3(-132)/4
x = -99
当 y = -132,从 ii,
z = 5(-132)/2
z = -330
结论,x = -99 ；y = -132 ；z = -330