Hello,
[tex]a\ \textgreater \ 0\ and\ b\ \textgreater \ 0 ==>a+b>0\\
a\ \textgreater \ b ==\ \textgreater \ a+b\ \textgreater \ b+b\\
==\ \textgreater \ a+b\ \textgreater \ 2b\\
==\ \textgreater \ 1\ \textgreater \ \dfrac{2b}{a+b} \\
==\ \textgreater \ \dfrac{1}{2} \ \textgreater \ \dfrac{b}{a+b} [/tex]