①(a²-b²／a²+2ab+b²)÷(2a-2b／a+b)
=[(a+b)(a-b)/(a+b)²]÷[2(a-b)/(a+b)]
=[(a-b)/(a+b)]÷[2(a-b)/(a+b)]
=1/2
②(a-1／a)÷(a-1／a²)
=(a-1／a)*(a²/a-1)
=a
②[(a-1)／a]÷[(a-1)／a]²
=[(a-1)／a]*[a/(a-1)]²
=a/(a-1)
=1-1/(a-1)