5x+7y=7x+5y+18

解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 5x+7y=7x+5y+18 (x+5y)(x-7y-1) 5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3.5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3先化简,再求值； 3x+5y-(x+y)=6 2(x+y)-3x=-7 3x-y+x=3 4【X-y-1】=3【1-y】-1 5x-4y+4x=3 2x+y-3x=11 【 x除以2 】-【y 除以3】 =2 2x+7y-3x=19 x+y+x=12 3x+2y-x=18 x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)= 3(x-y)把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)=3(x-y)²-4(x-y)+7(x-y)-6(x-y)²= 5(x+y-2)=3-y x+7分之18y=-七分之一 (3x-4y)(5x-4y)-(7x-8y)(6y-5x) 化简:3(x-y)²-7(x-y)+ 2(x-y)²+5(x-y) 已知5x=7y,则x:y=( ) ｛x+y=7 ｛2x-5y=-21 Y=x+3 7x+5y=9 5x+14=y,7x+4=y y-x=3 7x+5y=-9 y=x+3 7x+5y=9