{ x-y=3 2y 3(x-y)=11 ,得 { x= y=

x3+y3=100(x+y)(x^2-xy+y^2)=100因x+y=1所以x^2-xy+y^2=100(x+y)^2-3xy=1001-3xy=100xy=-33x^2+y^2=(x+y)^2-2x

x3+y3-x2y-xy2=(x+y)(x2-xy+y2)-xy(x+y)=（x+y)(x2-2xy+y2）=（x+y)（x2+2xy+y2-4xy）=（x+y）[(x+y)2-4xy]=10×（10

∵x+y=1，∴x3+y3+3xy=（x+y）（x2-xy+y2）+3xy=x2+y2+2xy=（x+y）2=1．

∵x+y+z=0,∴z=(-x-y)x^3+y^3+z^3=x^3+y^3-(x+y)^3=x^3+y^3-x^3-y^3-3x^2y-3xy^2=-3xy(x+y)=3xyz

x3+y3=（x+y）（x2-xy+y2），∴x2-xy+y2=10，∵x+y=10，∴x2+2xy+y2=100，∴2xy=100-（x2+y2），把xy=x2+y2-10，代入得：100-（x2+

24

y^2=x^3-3x^2+2xx^2=y^3-3y^2+2y两式相减得：y^2-x^2=(x^3-y^3)-3(x^2-y^2)+2(x-y)(x-y)(x^2+xy+y^2-2x-2y+2)=0所以

(x+y)³=x³+y³+3x²y+3xy².记忆方法：各立方,然后3x方y,3xy方(x+y)³=x³-y³-3x&#

（1）因为两个式子能合并同类项,∴相同字母的指数相同即a=2,b=1,∴a+b=3（2）x²+y²=（x+y）²-2xy=9-2=7（3）x²+3x+2=x&#

原方程可化为x（x+1）（x+2）+3（x2+x）=y（y-1）（y+1）+2，∵三个连续整数的乘积是3的倍数，∴上式左边是3的倍数，而右边除以3余2，这是不可能的．∴原方程无整数解．故选A．

(x+y)^3=X^3+3X^2Y+3XY^2+Y^3x^2y+xy^2=303x^2y+3xy^2=90x^3+Y^3=35

∵x+y=1∴x3+y3-xy=（x+y）（x2+y2-xy）-xy=x2+y2-2xy=（x-y）2≥0即x+y=1时，x3+y3-xy的值是非负数．

x^3+y^3+x^3y^3=12,x^3+y^3+x^3y^3+1=13,（x^3+1)(y^3+1)=13(x+1)(x^2-x+1)(y+1)(y^2-y+1)=13;x+y+xy=0,x+y+

x^3+y^3=(x+y)(x^2-xy+y^2)=10(x^2+y^2-xy)=100x^2+y^2-xy=10(1)x+y=10平方x^2+2xy+y^2=100(2)(1)*2+(2)2x^2+

根据题意得：x+y＝0①2x−3y＝5②，①×3+②得：5x=5，即x=1，将x=1代入①得：y=-1，则原式=1-1=0，故答案为：0

27.已知x=1.25,y=-0.64时,求[(x+y)3-(x3+y3)]÷(x+y)的值.[(x+y)^33-(x^3+y^3)]÷(x+y)解,得：==(x+y)^3*1/(x+y)-(x+y)

y=(1-C1-C2)y1(x)+C1y2(x)+C2y3(x)即y=y1(x)+C1*[y2(x)-y1(x)]+C2*[y3(x)-y1(x)]而y1(x),y2(x),y3(x)都是线性方程y'

1.y=C1e^x+C22x^+C32.(-2,0,3)33.1/(3倍根号下2）4.

x3+3xy-y3=(x-y)(x^2+y^2+xy)+3xy=-x^2-y^2+2xy=-(x-y)^2=-1

x²-x=7y²-y=7相减x²-x-y²+y=0(x+y)(x-y)=x-yx-y≠0约分x+y=1x²-x=7y²-y=7相加x&sup