Question

因式分解：(1)(x-y)(x2-xy+y2)+xy(y-x)。(2)-2xy-4x2y+2xy2.(3)3x2(a+3)-4x2y(a+3)求过程结果。

跟在字母后边的数字例如2是平方。数字在前面是数字。（5）a2-3a+2（6）(x-y)(x2-xy+y2)+xy(y-x) 请各位帮助。一定要有过程结果。
（1）若（x-y）2=49,x=y=5,求xy。（2）若x=1，y=2分之1,则x2+4xy+4y2的值是。（3）利用平方差公式计算（2x-5)(-2x-5)的结果是。（4）下列运算中正确的是（）A3a+2a=5a2 B(2a+b)（2a-b)=4a2-b2 C2a2乘a3=2a6 D(2a+b)2=4a2+b2 (5)若9x2-kxy+49y2是一个完全平方公式，那么K的值是多少？

Answer 1

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

(2)-2xy-4x^2y+2xy^2
=-2xy(1+2x-y)

(3)3x^2(a+3)-4x^2y(a+3)
=x^2(a+3)(3-4y)

a^2-3a+2
=(a-2)(a-1)

Answer 2

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

-2xy-4x²y+2xy²
=2xy(y-2x-1)

3x²(a+3)-4x²y(a+3)
=x²(a+3)(3-4y)

a²-3a+2
=(a-1)(a-2)

第6题和第1题一样

Answer 3

（1）=(x-y)（x2-xy+y2)-xy(x-y)
=(x-y)(x2-xy+y2-xy)
=(x-y)^3
(2)=-2xy(1+2x-y)
(3)=(a+3)(3x2-4x2y)
=x2(a+3)(3-4y)
(5)=(a-2)(a-1)
(6)同（1）

Answer 4

（1）·(x-y)(x2-xy+y2)-xy(x-y)=(x-y)(x2-xy+y2-xy)=(x-y)(x-y)2=(x-y)3