5/2(x+y)=1200 10/3(x-y)=1200的解5/2=5分之2 应用题来的 A市到B市的航线长1200KM，一架飞机从A市顺风飞往B市需2小时30分，从B市顺风飞往B市需3小时20分，求飞机的平均速度与风速。本人也不知方程组

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuaihuajian x-y/7 - x+y/10 =1/2 2(x-y)-5(x+y)=3修改、、、、（x-y)/7-(x+y)/10=1/2 2(x-y)-5(x+y)=3 5(x+y)-2x=0 3x-10(x+y)=2 {2X=5(X+Y) 3X-10(X+Y)=2 {2X=5(X+Y)3X-10(X+Y)=2怎么解? {2x=5(x y) 3x-10(x y)=2 3(2X+Y)+(2(2x-Y)=6 (8X+4y)-(10X-5Y)=2 已知x,y满足约束条件 2x+5y>=10 2x-3y>=-6 2x+y 已知x,y满足约束条件{2x+5y>=10,2x-3y>=-6,2x+y { x-y/7-x+y/10=1/2 {2(x-y)+5(x+y)=3 { x-y/7-x+y/10=1/2 {2(x-y)+5(x+y)=3 (4x-2y-z)-{5x-[8y-2z-(x-2y)]-x-(3y-10z)}=? 已知实数x,y满足2x+5y>=10;2x-3y>-6;2x+y 10/x+y+3/x-y=-5 15/x+y-2/x-y=-1（用换元法解此方程组） 解分式方程：10/(x+y)+3/(x-y)=-5,15/(x+y)-2/(x-y)=-1 3/(X-Y)+10/(X+Y)=-5 2/(X-Y)-15/(X+Y)=1 解分式方程组 ｛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