\[= \frac{b^{2} - 2b + 4}{(b + 2)(b^{2} - 2b + 4)} = \frac{1}{b + 2}\]
\[b = - 2,1:\]
\[\frac{1}{- 2,1 + 2} = \frac{1}{- 0,1} = - 10.\]