已知x+y=6,xy=7,试求x²+y²

题目写错应该是求（6xy+7y)+[8x-(5xy-y+6x)]（6xy+7y)+[8x-(5xy-y+6x)]=6xy+7y+8x-5xy+y-6x=xy+2x+8y=xy+2(x+4y)=5+2×

x/2=y/3x=2y/3所以x²-2xy-3y²/x²-6xy-7y²=(x+y)(x-3y)/(x+y)(x-7y)=(x-3y)/(x-7y)=(2y/3

xy^2=-6(xy^2)^2=(-6)^2即x^2y^4=36(xy^2)^3=(-6)^3即x^3y^6=-216-xy(x^3y^7-3x^2y^5-y)=-xy[(x^3y^6)*y-3(x^

因为x+y的平方=X平方+2XY+Y的平方所以X+Y的平方-2XY=X的平方+Y的平方将X+Y=6.XY=7代入得6*6-2*7=22

因为x/y=2所以x=2y是[x^2-xy+3y^2]/[x^2+xy+6y^2]吧=(4y^2-2y^2+3y^2)/(4y^2+2y^2+6y^2)=5y^2/12y^2=5/12

5xy+4x+7y+6x-3xy-4xy+3y=5xy-3xy-4xy+4x+6x+7y+3y=（5-3-4）xy+（4+6）x+（7+3）y=-2xy+10x+10y=-2xy+10（x+y）因为x

解题思路：本题是求整式的值，注意一定要先化简，再求值。化简就是先去括号，在合并同类项。解题过程：解：（6xy+7y）+[8x-（5xy-y+6x）]=（6xy+7y）+[8x-5xy+y-6x]=6x

原式=6xy+7y+8x-5xy+y-6x=xy+2x+8y=xy+2(x+4y)=···再问：还有些题哈……

原式=6xy+7y+8x-5xy+y-6x=xy+8y+2x=xy+2(x+4y)=5+2×(-1)=3

6xy+7y）+【8x-（5xy-y+6x）】=xy+8y+2x=xy+2(4y+x)=5-2=3

原式=6xy+7y+8x-5xy+y-6x=xy+2(4y+x)=5-2=3

（6xy+7y)+[8x-(5xy-y+6x)]=6xy+7y+（8x-5xy+y-6x）=6xy+7y+8x-5xy+y-6x=（6xy-5xy）+（7y+y）+（8x-6x）=xy+8y+2x=x

6xy+7y+[8x-5xy+y-6x]=6xy+7y+8x-5xy+y-6x=(6xy-5xy)+(7y+y)+(8x-6x)=xy+8y+2x=xy+2(4y+x)=5-2=3再问：请问x=？y＝

x^2y+xy^2=xy（x+y）=7x6=42再问：��(x+1)^2=13��x^2+2x+3=再答：x^2+2x+3=（x+1）^2+2=13+2=15

先把代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)化简（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)=5XY+4X+7Y+6X-3XY-4XY+3Y=-2XY+10X+1

最简单的方法就是用特殊值,令x=-2,y=1然后代入所求表达式,求出其值.为-8；另外此内题的另一个解法是变化所求表达式,使它变成关于xy^2的表达式.

xy/x+y=6∴xy=6(x+y)3x-2xy+3y/-x+3xy-y=[3x-12(x+y)+3y]/[-x+18(x+y)-y]=-9(x+y)/17(x+y)=-9/17再问：你在啊？再答：在

原式=x^4y^8-3x³y^6-11.5xy²=(xy²)^4-3(xy²)³-11.5(xy²)=1296+648+69=2013

不会

[(x-y)^2+2xy-y^2]/[x^2+7xy+y^2]=[x²-2xy+y²+2xy-y²]/[x^2+7xy+y^2]=x²/[x^2+7xy+y^2