7x+1=3y4x+17=5y

min=7x+5x4x+3y-20≤0x-3y-2≤0x,y≥0min=7x+5y4x+3y-20≤0x-3y-2≤0y 若4x-3y=0且x≠0，y≠0，则4x−5y4x+5y的值为（　　） x+y=3 x+2y=9 3/x+1=y y-x=3 y=2x-3 y-3x=1 2(x+1)-y=6 7x-5y=-9 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y 7x-3y/5=5x-y/3-x+y/2 x-1/5=y+1/3 换元法解方程组3/x+y+2/x-y=17/5 2/x+y-5/x-y=1 { x-y/7-x+y/10=1/2 {2(x-y)+5(x+y)=3 已知：x-y=1,x+y=-7,求代数式3（x+y)+20(x-y)-5的值 解方程组x/4+Y/4=2,x/6+y/3=2; X+2Y=1,2X-3Y=2; 4X-3Y=17,5X+Y=7 解方程组:①3x-7y=1,5x-4y=17②23x+17y=63,17x+23y=57 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1