1.2m^3 - 8m =2m(m^2-4)=2m(m-2)(m+2) 
2.(x+2)(x+4)+ x^2 -4 
=(x+2)(x+4)+(x-2)(x+2) 
=(x+2)(2x+2)=2(x+2)(x+1) 
3.4(x-y)^2 - 2(y-x)^3 = 
4(x-y)^2 +2(x-y)^3= 
(x-y)^2(4+2x-2y) 
4.x^2 (y^2 - 1)+2x(y^2 - 1)+(y^2 - 1)= 
(y^2 - 1)(x^2+2x+1)=(y^2 - 1)(x+1)^2 
a(x-y)-b(y-x)+c(x-y) 
=a(x-y)+b(x-y)+c(x-y) 
=(x-y)(a+b+c 
3 x^3 y - 6xy + 3y 
=3y(x^3 - 2x + 1) 
=3y(x^3 - x^2+ x^2 -2x + 1) 
=3y(x-1)(x^2+x-1) 
x^3 + 6x^2 - 27 
=X立+3X方+(3X方-27) 
=X方(X+3)+3(X+3)(X-3) 
2a-b)^2+8ab 
(2a-b)^2+8ab=4a^2-4ab+b^2+8ab 
=4a^2+4ab+b^2 
=(2a+b)^2 
(x+2)(x+3)+ x^2 +4=X方+5X+6+X方+4 
=2X方+5X+4 
=(X+2)(2X+2) 
xy-x-y+1 
=x(y-1)-(y-1) 
=(x-1)(y-1) 
=(X+3)(X方+3X-9) 
a^2 - 2ab + b^2 -1=(A-B)方-1 
=(A-B+1)(A-B-1) 
计算:(1-1/2^2)=(1-1/2)(1+1/2)=1/2*3/2 
(1-1/3^2)=(1-1/3)(1+1/3)=2/3*4/3 
...
(1-1/9^2)=8/9*10/9 
(1-1/10^2)=9/10*11/10 
(1-1/2^2)(1-1/3^2)(1-1/4^2)...(1-1/9^2)(1-1/10^2) 
=1/2*3/2*2/3*4/3*...*8/9*10/9*9/10*11/10 
=1/2*11/10 
=11/20 
2010^2 - 2009^2 + 2008^2 - 2007^2 +...+ 2^2 - 1^2=2011(2010-2009+2008_2007+...+2-1)=2011*1005=2021055
27^2-46*27+ 23^2
=27^2-2*23*27+ 23^2
=(27-23)^2=25
a^2 + b^2 + 2a-4b+5
=(a^2+ 2a+1)+( b^2-4b+4)
=(a+1)^2+(b-2)^2=0
a+1=0 b-2=0
a=-1 b=2
4a^2 + b^2 =4ab
4a^2 + b^2 -4ab=0 两边通除以非负数a^2
(b/a)^2-4b/a+4=0 b/a=2
