80(1-x)y-搜答案-搜狗做题网

3(x+y)+3(y-x)=1(1)3(x+y)+4(y-x)=-1(2)(2)-(1)得y-x=-2(3)代入（1）3（x+y)-6=1x+y=7/3=>x=7/3－y又由（3）得x=y+2y+2=

(1)由原方程化简得x+y=420①,0.3x+0.4y=128②①-②×2.5得x-0.75x=420-3200.25x=100x=400把x=400代入①得y=20∴x=400,y=20（2）由原

xy-1+x-y

xy-1+x-y=XY+X-Y-1(加法交换律）=（XY+X）－（Y＋1）＝X（Y＋1）－(Y+1)（提取公因式X）=(Y+1)(X-1)（提取公因式Y+1）这样可以么?

1/9x^2-10/9xy+y^2-(1/9x^2-y^2)=-10/9xy+2y^2=2y(y-5/9x)

xyx+yyx+yxx+yxyc1+c2+c32(x+y)yx+y2(x+y)x+yx2(x+y)xyr3-r2,r2-r12(x+y)yx+y0x-y0-yy-x--此时用对角线法则得=2(x+y)

1、(x-2y)(x+y)

原式=x^2-xy-2xy-2y^2=2x^2-3xy-2y^22、是的,你算错了,以后要细心!原式=(a^2+4ab+4b^2)(2a+b^2)=2a^3+a^2b^2+8a^2b+4ab^3+8a

x=1880y=1800

-1∠x+y

设m=x+y,n=x-y,则x=（m+n）/2,y=(m-n)/2,则Z=m+n-3/2*（m-n）=5n/2-m/2,所以:3＜z＜8.

1)x(x-y)(x+y)-x(x+y)^2=x((x-y)(x+y)-(x+y)^2)=x(x^2-y^2-x^2-2xy-y^2)=x(-2xy-2y^2)=-2xy(x+y)2)（2a+b)(2

1、y-x/x²-y²

11/x+y2-1

[(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y=[x²-y²-x²-2xy-y²-xy+xy²]/(y/2)=[(x-2)y

(1)(x+y)^2-(x-y)^2

1)4xy2)-1/5y^23)2ab^2c4)(2a+b)^25)2yz+xz6)-3a-57)4xy

1.1/x+1/y=(x+y)/xy=-1/(x+y)去分母可得,（x+y)^2+xy=0即x^2+y^2=-3xy所以y/x+x/y=(x^2+y^2)/xy=-32.由1/x-1/y=5可得y-x

1)(2x+5y)(2x-5y)(-4x^2-25y^2)=-(4x^2-25y^2)(4x^2+25y^2)=-(16x^4-625y^4)=625y^4-16x^42)[（x+y)(x-y)-(x

(1)(x^2/x)-y-x-y

（1)x^2/x)-y-x-y=x-y-x-y=-2y(2)(a/a-b)-(a/a+b)-(2b^2/a^2-b^2)=a(a+b-a+b)/(a^2-b^2)-(2b^2/a^2-b^2)=2b/

解(x-y)(x+y)-(x-2y)²+x(3x-5y)-(x-y)(x-2y)=(x²-y²)-(x²-4xy+4y²)+(3x²-5xy

y=[x-1],

取整

1 ,化简（x-y)(x+y)

（x-y)(x+y)=x²-y²（x+3)²=x²+6x+9(x-1)(x-2)=x²-3x+2√25=5

x-y+1

变形为y＞x+1,在坐标系中表示直线y=x+1上方的部分再问：为什么y＞x+1就表示直线y=x+1上方的部分啊，是规定的吗再答：y表示函数值，在坐标系中y=x+1这一函数关系表示直线即直线上每个点的横