x+y=70 2x-4y=80怎么解,

4x方y/(x-2y)(x+2y)怎么算[x方/x-2y]-4x方y/(x-2y)(x+2y)=? x+y=70 2x-4y=80怎么解, {80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 怎么解( ⊙ o ⊙ {80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 快 急 由X/Y=2Y/X-Y 怎么解得x=2y? 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y怎么解 2x=y 3y=x怎么解 (x/y)2-(x/y)=1怎么解? ｛x/60+y/80=10,x/60+y/40=15、｛2x/3+3y/4=1/5,5x/6-5y/2=2、｛5/2(x+y）=1200,10/3（x+y）=1200｛4x+5y=98,5y-4x=2、｛x/3+y/4=54/60,y/4+x/5=42/60怎么解?{40-y=x-4 40-y=y-x y'=x+2y+1/2x+4y-1这个微分方程怎么解啊? x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x^2-4xy+3y^2=（x-3y)(x-y)x^2-4xy+3y^2 怎么分解成（x-3y)(x-y) X+Y=5.7 1/4X+2/5Y=4/5X 怎么解 X+y=20 90x- 80x+60y-50y=260 怎么解 5x+4y=22 4x+y=3y+x 怎么解 X+y=15 2x-y=5y-x怎么解 二元二次方程(x+y)(x-2y)=-5,(x-y)(x+2y)=7 怎么解 二元一次方程(x+y)/2+(x-y)/3=6,4(x+y)-5(x-y)=2怎么算 已知2x-y=10,求式子[(x^2+y^2)-(x-y)^2+2y(x-y)]/4y (4xy-2y²)/4y是怎么变成=2y(2x-y)÷4y