x 0 1 2 3 y 40 35 30 25 并说明为什么

{4x-3y-10=0 3x-2y=0,{3x-4(x-y)=2 2x-3y=1,{2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 已知2x-y=0,求分式【1+（3*y*y*y/x*x*x-y*y*y）】/【1+（2y/x-y）】的值注：x*x*x-y*y*y=（x-y）*（x*x+xy+y*y） （1）x+y=420,30%x+40%y=160×80% （2）x-y/7-x+y/6=1/2,2(x-y)-5(x+y)+1=0,求方程组解嗷嗷嗷! 帮我做2道数学方程（1）6x-7y-40=0 5y-2x+8=0（2）（x+y)/2+(x-y)/3=6 2(x+y)-(x-y)=-4 帮我做2道数学方程（1）6x-7y-40=0 5y-2x+8=0（2）（x+y)/2+(x-y)/3=6 2(x+y)-(x-y)=-4 帮我做2道数学方程（1）6x-7y-40=0 5y-2x+8=0（2）（x+y)/2+(x-y)/3=6 2(x+y)-(x-y)=-4 {x+y=1 ,xy=-6{x(2x-3)=0,y=x²-1{(3x+4y-3)(3x+4y+3)=0,3x+2y=5{(x-y+2)(x+y)=0,x²+y²=8{(x+y)((x+y-1)=0,(x-y)(x-y-1)=0 2x+y-2=0,x-3y-1 30x=4/5y 40（x-1）=y+25 1/3（x+y)=33-1/2x=2(3-1/2y) 1.6x=5y300+4x+100=4y2.4(x+y)=805(x-y)=803.y-x=45(85%y-x)8=(y-35-x)x24.0.7(1+40%)x+0.9(1+40%)y=399(1+40%)x+((1+40%)y=4905.x+y/2=502/3x+y=506.x+y=3002.89%乘3x+2.7%乘3y(1-20%)=32338.2-30000 A={(x,y)|y=-x^2+mx-1},B={(x,y)|y=3-x,0A={(x,y)|y=-x^2+mx-1},B={(x,y)|y=3-x,0 2x(2x+3y)-y(x-3y),其中(2x-1)^2+|2-y|=0 若x,y满足|2x-y-3|+|3x+2y+1|=0,则x= y= 若x,y满足|x-y+1|+(x+y+3)^2=0则x^2-y^2= 关于x,y的方程组x+y=k-2,2x-3y=1中,x>0,y 关于x,y的方程组x+y=k-2,2x-3y=1中,x>0,y 求导数y=3x-x^2 求y',y'/ x=1 y'/x=0 已知M={(x,y)|y=-x^2+mx-1},N={(x,y)|y=-x+3,0