1.2(x-3)/(2-x)^2 除以 (x-3) 乘以 (x+3)(x-2)/3-x =2(x+3)/(x-2)(3-x) =2x+6/(x-2)(3-x)
2.[(a^2+b^2)/(a^2-b^2)-(a-b)/(a+b)]/[2ab/(a-b)(a+b)^2]
=[(a^2+b^2-(a-b)^2)/(a^2-b^2)]/[2ab/(a-b)(a+b)^2]
=2ab/(a^2-b^2)/[2ab/(a-b)(a+b)^2]
=(a-b)(a+b)^2/(a+b)(a-b)
=a+b
当a=1,b=2时,原式=3