Ответ:
Объяснение:
1. (mn-m²)/(m²+n²)=m*(n-m)/(m²+n²)=-m*(m-n)/(m²+n²)).
2.m/(m+n)+n/(m-n)=(m*(m-n)+n*(m+n))/((m-n)(m+n))=
=(m²-mn+mn+n²)/((m-n)(m+n))=(m²+n²)/((m-n)(m+n)).
3. -m*(m-n)/(m²+n²))*(m²+n²)/((m-n)(m+n))=
=-m*(m-n)*(m²+n²)/((m²+n²)*(m-n)(m+n))=-m/(m+n).