3x+3y=30-3 (30-5x)*2=30-5y 这个方程怎么解

{3x+4y=39-2y 5x+3y=2x+30 {3x+4y=39-2y 5x+3y=2x+30 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) x+y/2+x-y/6=5 2(x+y)-3(x-y)=-2 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 2Y：30%=3X：50%求X:Y （x+y-5)*（x+y-5)+（x-y+3)=0 x*x-y*y 先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5 已知:3x-5y=0,求x/y,x-y/y,x-y/x 5（x+y)+3(x-y)=90 5(x+y)-3(x-y)=30,解二元一次方程组 15/(X+Y)=0.5 15/(X-Y)=3能得出x+y=30 x-y=5? {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 方程组：第一题（5+1）x=5y 第二题x-y/3=x+y/2 4y-4x=30+10 2x-3y=7（5+1）x=5y x-y/3=x+y/2 4y-4x=30+10 2x-5y=7 上面那个题目错的 3（x+y)+2(x-3y)=20,30%x+60%y=10%*60