3y=7-2x 3x=7+5y

若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 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 {2x+y/3-2y=0 2(2x+y)-5=7y 7x-3y/5=5x-y/3-x+y/2 x-1/5=y+1/3 解二元一次方程组:{5(x+y)+3(x-y)=2{7(x+y)-3(x-y)=-6 { x-y/7-x+y/10=1/2 {2(x-y)+5(x+y)=3 {5x-2y=7y+2x 3x+2y=22 7x-3y/5=5x-y/3-x+y/2 x-y/3=x+y/2 2x-5y=7等于多少 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 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