2x-11y=-7,3x y=7,则x等于

已知x/y=7/2,(2x²+3xy+2y²)/(x²+2xy+y²)=(2x/y+3+2y/x)/(x/y+2+y/x)=(2×7/2+3+2×2/7）/（7

(x^2-3XY+2Y^2)/(X^2-2XY+Y^2)=(x-2y)(x-y)/(x-y)^2=(x-2y)/(x-y)=(x-y-y)/(x-y)=1-y/(x-y)=1-1/(x/y-1)=1-

x^2+y^2=7,xy=-25x^2-3xy-4y^2-11xy-7x^2+2y^2=-2x^2-14xy-2y^2=-2(x^2+y^2)-14xy=-2*7-14*(-2)=-14+28=14

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^

已知xy^2=-2那么-xy(x^3y^7-3x^2y^5-y)=-x^4y^8+3x^3y^6+xy^2=-(-2)^4+3*(-2)^3+(-2)=-16-24-2=-42如果不懂,请Hi我,祝学

楼主算得对,第一个回答在第二步的地方把三次方的系数3弄丢掉了,所以正确的还是-165

5x²-3xy-4y²-11xy-7x²+2y²=-2x²-2y²-14xy=-2(x²+y²)-14xy=-2×7-1

原式=6x+4xy+2xy+3x+2y-4xy+7y=9x+9y+2xy=9(x+y)+2xy=9×4+2×2=36+4=40

（4xy+12y)+[7x-(3xy+4y-x)]=4xy+12y+7x-3xy-4y+x=xy+8x+8y=xy+8(x+y)=(-2)+8*3=-2+24=22

xy（2x^3y^7+5x^2y^5-y)=xy[2y(xy^2)^3+5y(xy^2)^2-y]=xy[2y(-2)^3+5y(-2)^2-y]=xy(-16y+20y-y)=3xy^2=3*(-2

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.

原式=-2x^2-2y^2-3xy-11xy=-2*7-14*(-1)=0

设X=kY.kY^2/(3k+2)Y=1/8kY^2/((2k+3)Y=1/7由上式得：3k+2=8kY,2k+3=7kY所以2/（8Y-3）=3/（7Y-2）所以Y=1/2,X=1

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

5x^2-(3xy+4y^2)-(11xy-2y^2)-7x^2=5x^2-3xy-4y^2-11xy+2y^2-7x^2=-2x^2-2y^2-14xy=-2(x^2+y^2)-14*xy=-2*7

因为x-y=-2xy所以将x-y都换成-2xy了

5X²-3XY-4Y²-11XY-7X²+2Y²=-2X²-2Y²-14XY=-2(X²+Y²)-14XY将X²

因为,x-y=3xy所以：-3x+6xy+3y/[(7x-5y)-9xy-(3x-y)]=[-3(x-y)+6xy]/[(7x-5y)-9xy-(3x-y)]=[-3*3xy+6xy]/[7x-5y-

[(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

x²＋y²=7转成x²=7-y²将xy=-2和x²=7-y²代人（5x²-3xy-4y²-11xy-7x²+2