1、(x^2-4y^2)/(x^2+4xy+4y^2)÷(x^2+xy-6y^2)/(x^2+5xy+6y^2)
=(x+2y)(x-2y)/[(x+2y)^2]÷[(x+3y)(x-2y)]/[(x+3y)(x+2y)]
=(x-2y)/(x+2y)÷(x-2y)/(x+2y)
=1
2、m等于它的倒数
m=1或者m=-1
(m^2+m-6)/(m-2)÷(m+3)/(m^2-3m+1)
=(m+3)÷(m+3)/(m^2-3m+1)
=(m^2-3m+1)
当m=1时原式=-1
当m=-1时原式=5
3、1/(3-x)=(2-x)/(x-3)+1
1=x-2+3-x(x不等于3)
当x不等于3时,式子恒成立