а) ((a-b)/a(a+b) - a/b(a+b)) :( (1/(a+b) + b²/a(a² -b²)) = (1/(a+b)) *(a-b -a) :
(b(a-b) -a²)/ab(a+b) : (a(a-b) +b²)/a(a-b)(a+b)=
=(ab -b² -a²)/ab(a+b) *a(b-a)(a+b)/(-a² +ab-b²) =(b-a)/b.
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б) ( (2ab/(a-b)(a+b) +(a-b)/2(a+b) )*2a/(a+b) -b/(a-b) =
((4ab +(a-b)²)/2(a-b)(a+b))*2a/(a+b) -b/(a-b) =(a+b)²/2(a-b)(a+b)* 2a/(a+b) -b/(a-b)=
=a/(a-b) -b/(a-b) =(a-b)/(a-b) =1