5X/3+4Y=10.4 ,3X/4+0.5Y=39/20

（5x+3y)(3y-5x)-(4x-y)(4y+x)= 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 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( 数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y -5(x-2y)^20 -4(5x-13y)^39 +3(5x-13y)^39 -20(x-2y)^20 其中 x=5 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuai 解方程组：（0.2x+0.1y）/2- （4x-y）/10=（x-y）/5+ (3x+0.5y)/30 (3x+2y-1 5x=y,5:y=x,3x=4y,3:x=4:y,3;x=y:4,3x+4x=y,3x+4=y y和x成比例吗