\[\frac{a}{a + 2b}\ \ и\ \ \frac{- 2b}{2b - a} = \frac{2b}{a - 2b}\]
\[Общий\ знаменатель:\]
\[(a + 2b)(a - 2b) = a^{2} - 4b^{2}.\]
\[\frac{a^{\backslash a - 2b}}{a + 2b} = \frac{a^{2} - 2ab}{a^{2} - 4b^{2}};\]
\[\frac{2b^{\backslash a + 2b}}{a - 2b} = \frac{2ab + 4b^{2}}{a^{2} - 4b^{2}}.\]