x(y^2-1)dx y(x^2-1)dy=0-搜答案-神马作文网

将方差的公式D(x)=Ex^2-(Ex)^2代入化简,中间要利用到1如果x,y独立的话Exy=ExEy2D(x)=Ex^2-(Ex)^2>=0两个结论剩下的就是整理化简了再问：我就是这样做的，没做出来

原式=1/2x-[1/(x+y)][(x+y)/2x-(x+y)]=1/2x-[1/(x+y)](x+y)(1/2x-1)=1/2x-(1/2x-1)=1/2x-1/2x+1=1

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

y=(x^2+x)/(x+1)

这样算,分离变量:x²+x=(x+1)²-(x+1)然后,除下来,就等于x+1-1=x注意,x≠-1!

A＝10x^2-6xy+3y^2B＝Zx^2＋Dxy+Vy^2C＝15y^4-36xy^3+62x^2y^2-20x^3y那就好办了对应项全相等就好3V=15-6V+3D=-3610V-6D+3Z=6

（x+2)(x+3)=x²+5x+6(x-4)(x+1)=x²-3x-4(y+4)(y-2)=y²+2y-8(y-5)(y-3)=y²-8y+15x²

应该很简单吧用等比性质,即使去掉条件3X=4Y也可以得到a/c=1/d=b/e=9/7即可a=9,b=18,c=7,d=7/9,e=14

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

[(-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

y=3/(x+1/x+1)x+1/x≤-2,所以x+1/x+1≤-1令t=x+1/x+1,则t≤-1,y=3/t值域为[-3,0)再问：你写的我看不大懂再问：一步步写再答：

=1/2x-1/(x+y)×[(x+y)/2x-(x+y)]=1/2x-1/2x+1=1/x+1=(x+1)/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

3(x+y)-4(x-y)=4(x+y)/2+(x-y)/6=1令a=x+y,b=x-y3a-4b=4(1)a/2+b/6=1则3a+b=6(2)(2)-(1)5b=2b=2/5a=(6-b)/3=2

4x=9yx=9/4*y(1)(x+y)/y=[(9/4)y+y]/y=(9/4+1)y/y=9/4+1=13/4(2)(y-x)/2x=[y-(9/4)y]/[2*(9/4)y]=(1-9/4)y/

结果为1