y=x*[30+(90-x)]-60*[30+(90-x)]怎么解

x+x+x+y=60 .x-y=4 x+x=y+30 x+y=450;40%x+30=60%y {x+y=450,60%y-40%x=30 5（x+y)+3(x-y)=90 5(x+y)-3(x-y)=30,解二元一次方程组 3（x+y)+2(x-3y)=20,30%x+60%y=10%*60 X+y=20 90x- 80x+60y-50y=260 怎么解 请问60%x+20%y=30%(x+y) 怎么得到x:y=1:3 y=x*[30+(90-x)]-60*[30+(90-x)]怎么解 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 {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=20时y=66 X=30时y=50X=40时y=40x=50时y=33x=60时y=28x=70时y=25x=80时y=22x=90时y=20求公式 化简 x / y(x+y) - y / x(x+y) = 已知x、y、z是正整数,求解下列联立方程 （x-y)(y-z)(z+x)=-90 (x-y)(y+z)(z-x)=42 (x+y)(y-z)(z-x)=-60 y=x(x x+x+x+y=42 x+y+y+y=30 求x=( )y=( ) x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空