(1/а-в - 1/а+в) : 2а/а-в=

(1/(а-b)-1/(a+b)):2a/(a-b)=(1/(a-b)-1/(a+b))*a-b/2a=1(a+b)-(1(a-b))/(a+b)(a-b)*a-b/2a=2b/(a+b)(a-b)*a-b/2a=b/(a+b)(a-b)*a-b/a=b/a+b*1/a=b/(a+b)*a=b/a(a+b)