3X=2y 9x+4y=4503X=2y 9x+4y=450 像这样的题这么做呢. 给说详细点好吗第一个式子左右乘以3 是什么意思阿

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 （x+y）/2- x-y/2=6 3(x+y)=4(x-y) x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 9y=3x-(x-1),4(x+y)-(2x+4)=8y 先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5 根据3（x+y)-2(x-y)=11,4(x+y)+3(x-y)=9可得出x+y= ,x-y= (x+y)(x-y)+(x-y)平方-(x-y)(3x-y) 其中x=-2 y=3分之一 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y)