1.(-4m^2+n^2)÷(2m+n)
=(n^2-4m^2) ÷(2m+n)
=(n+2m)(n-2m)÷(2m+n)
=n-2m
2.(x^2-4x+4)÷(1-1/2x)
=(x-2)^2÷[1/2*(2-x)]
=(2-x)^2÷[1/2*(2-x)]
=(2-x)÷(1/2)
=2*(2-x)
=4-2x
3.(1-81x^4)÷(1+3x)÷（1+9x^2)
=(1-9x^2)(1+9x^2)÷(1+3x)÷（1+9x^2)
=(1-9x^2)(1+9x^2)÷[(1+3x)*（1+9x^2) ]
=(1-9x^2)÷(1+3x)
=(1-3x)(1+3x)÷(1+3x)
=1-3x
解方程：
4.(2x-1)(x+3)=0
x=1/2或x=-3
5.2x^2+3x=0
x(2x+3)=0
x=0或x=-3/2
6.(x+5)^2=1
(x+5)^2-1=0
(x+5-1)(x+5+1)=0
(x+4)(x+6)=0
x=-4或x=-6
7.(2x+1)^2=(1-x)^2
(2x+1)^2-(1-x)^2=0
[(2x+1)-(1-x)][(2x+1)+(1-x)]=0
(2x+1-1+x)(2x+1+1-x)=0
3x(x+2)=0
x(x+2)=0
x=0或x=-2
8.-0.2x^2+5x=0
-x^2+25x=0
x^2-25x=0
x(x-25)=0
x=0或x=25
9.(2-x)^2=4(x+3)^2
(2-x)^2-4(x+3)^2=0
[(2-x)-2(x+3)][(2-x)+2(x+3)]=0
(2-x-2x-6)(2-x+2x+6)=0
(-3x-4)(x+8)=0
(3x+4)(x+8)=0
x=-4/3或x=-8