{x+y=420,30%x+40%=160×80%解方程

x+x=y+30 X+Y=40,(X*Y)/(X+Y)=7.5 x+x+x+x+y=40 x+y= 13x=y= x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x+y=450;40%x+30=60%y {x+y=450,60%y-40%x=30 40X+30Y=2200 X>20 Y 化简 x / y(x+y) - y / x(x+y) = （1）x+y=420,30%x+40%y=160×80% （2）x-y/7-x+y/6=1/2,2(x-y)-5(x+y)+1=0,求方程组解嗷嗷嗷! y=x(x 初二上学期方程题 4x+y=5 5x+4y=63x-2y=1 2x+3y=13x-2y=7 7x+5y=32x+3y=17 2x-y=-4x+5y=6 2x+y=23x-6y=4 3x+2y=52x+y=73x-4y=53x+y=1x-2y=-1x+y=42x+3y=92x-3y=74x+5y=3x+y=20004x+6y=90003x+5y=113x-2y=42x+3y=215x-2y=5x+y=54x+3y=182x+3y=16x+4y=132x+3y=40x x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空 x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 {6/x+y+10/x-y=30 6/x+y-10/x-y=-1 x+y=30,x方+y方=458,求x,y求x,y x+x+x+x+y+y+y=56 x+x+x+y=42 x+y+y+y=30 求x=( )y=( ) 怎么解这方程Y/(X+Y)=40% Y/(X+Y+5)=30%