几道初二数学题！！！

1、
(a+15)/(2a+6)-(a²-81)/(a²+6a+9) ÷(a-9)/(a+3)
=(a+15)/2(a+3)-(a+9)(a-9)/(a+3) ²×(a+3)/(a-9)
=(a+15)/2(a+3)-(a+9)/(a+3)
=(a+15-2a-18)/2(a+3)
=-(a+3)/2(a+3)
=-1/2
2、
[(a-4)/(a²-4a+4)-2/(a-2)] ÷(a²+2a)/(a+3)
=[(a-4)/(a-2) ²-2(a-2)/(a-2) ²]×(a+3)/a(a+2)
=(a-4-2a+4)/(a-2) ²×(a+3)/a(a+2)
=-a/(a-2) ²×(a+3)/a(a+2)
=-(a+3)/(a-2) ²(a+2)

1、
1/x+2/(x-1)=2/(x²-x)
1/x+2/(x-1)=2/x(x-1)
x-1+2x=2
3x=3
x=1
因X＝1时，X-1＝0
则X＝1为方程的增根

2\
1/(2x+3)-1/(2x-3)=4x/(4x²-9)
2x-3-2x-3=4x
4x=6
X=3/2
因X＝3/2时，2X-3＝0
则X＝3/2为方程的增根

亲，是化简还是因式分解？

什么意思？