(a²-b²)/(a²-ab)÷(a²+2ab+b²)/a
=[(a+b)(a-b)]/[a(a-b)]÷(a+b)²/a
=(a+b)/a×a/(a+b)²
=1/(a+b)
=1/[(-1/2)+(-1)]
=1/(-3/2)
=-2/3