求方程组的解 {x+y=450 1 {60%x-40%=30 2{2x+2y=1{x-6y=1
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x+y=450(1)
60%x-40%y=30(2)
60x-40y=3000
3x-2y=150(3)
2x+2y=900(4)
(3)+(4) 5x=1050
x=210y=450-x=450-210=240
x=210y=240(2) 2x+2y=1(1)
x-6y=1(2)
2x-12y=2(3)
(1)-(30 14y=-1
y=-1/14
x=1+6y=1-3/7=4/7
x=4/7,y=-1/14