原式=[(a²+b²)/a²b²+2/(a+b)*(a+b)/ab]×ab/(a²+2ab+b²)
=[(a²+b²)/a²b²+2/ab]×ab/(a²+2ab+b²)
=(a²+2ab+b²)/a²b²×ab/(a²+2ab+b²)
=1/(ab)
原式=[(a²+b²)/a²b²+2/(a+b)*(a+b)/ab]×ab/(a²+2ab+b²)
=[(a²+b²)/a²b²+2/ab]×ab/(a²+2ab+b²)
=(a²+2ab+b²)/a²b²×ab/(a²+2ab+b²)
=1/(ab)