\[\frac{2b}{2b + c} - \frac{4b^{2}}{4b^{2} + 4bc + c^{2}} =\]
\[= \frac{2b^{\backslash 2b + c}}{2b + c} - \frac{4b^{2}}{(2b + c)^{2}} =\]
\[= \frac{2bc}{(2b + c)²}\]