2x+3y=15 (x+1)/7=(y+4)/5二元一次方程 2x＋3y=15 x＋1/7=y＋4/5

已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 例X=1 y=21.X+Y=5 X-Y=15 2.2X+3Y=4 5X+6Y=7 3.X+3Y=5 3X+Y=-1 4.2X+Y=3 3X+5Y=11 5.4X+3Y=6 2X+Y=4 6.X+Y=180 X=3Y-10 7.3X-2Y=3 2X-Y=7 8.5X+3Y=7Y X+Y=45 9.3X+4Y=126X+8Y=24 X:6Y=1:4 10.X+Y=138 X-45=Y+53 11.X+Y=60 14Y=20X 12.2X+3Y=15.5 5X+6Y=35 13.X+Y=170 3 x^2+y^2=15,x+y=7,x＞y,求x-y 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 x+2y=2x+y+1=7x-y 求：2x-y? (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 变量x,y满足约束条件,x+y>=3,x-y>=-1,2x-y (x-y)^2+(x+y)(x-y) 其中 X =3 Y=-1 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x-3y=2x+y-15=1