(1/а + 1/b)* 2ab/(a²-b²)=(b+a)/ab * 2ab/((a+b)(a-b))=2/(a-b)
(1/(m-n) - 1/(m+n)) : 2/(3m-3n)=(m+n-m+n)/((m-n)(m+n)) * 3(m-n)/2=2n/(m+n) * 3/2=3n / ((m+n)
a - ((a²-5a)/(a+1)) * 1/(a-5)=a - ((a(a-5)/a+1) * 1/(a-5))=a - (a/a+1)=(a(a+1)-a)/(a+1)=(a²+a-a)/(a+1)=a²/(a+1)
(x²-y²)/xy : (x-y)/3y * 1/(x+y)=((x-y)(x+y))/xy * 3y/(x-y) * 1/(x+y)=3/x