分类：教育/科学-学习帮助
问题：帮我做下这几个题`!1.已知a
1.已知a-b=5√2,a-c=√2,则b^2+c^2-2bc=________.

2._______=-2x(3a+2b+c).

3.已知(mx-y)(x+y)=2x^2+nxy-y^2,则m=_____,n=____.

4.如果x+y=5,xy=0,则x^2y+xy^2=______,x^2-xy+y^2=_______.




因式分解:

1.x^(n)-x^(n-1)    ←(x的n次方,减去x的n-1次方)


2.9(x-y)^2-16(x+y)^2
回答：
 
1.已知a-b=5√2,a-c=√2,
     ===>b-c =4√2
则b^2+c^2-2bc=(b-c)^2  =32

2.-6ax-4bx-2cx=-2x(3a+2b+c). 

3.已知(mx-y)(x+y)
      =mx^2+(m-1)xy-y^2
       =2x^2+nxy-y^2,
      则m=2 n= 1 

4.如果x+y=5,xy=0,
   则x^2y+xy^2=xy(y+x)=0
  x^2-xy+y^2=(x+y)^2-3xy =25

1.x^(n)-x^(n-1)  =[x^(n-1)](x-1)


2.9(x-y)^2-16(x+y)^2 
  =[3(x-y)]^2 -[4(x+y)]^2
 =[3(x-y)+4(x+y)][3(x-y)-4(x+y)]
 =(7x+y)(-x -7y)
=-(7x+y)(x+7y)