Подставим значение $$k=-\frac{4}{5}$$ в выражение $$-k(5-k)-(1+k)^2$$:
$$-(-\frac{4}{5})(5-(-\frac{4}{5}))-(1+(-\frac{4}{5}))^2 = \frac{4}{5}(5+\frac{4}{5})-(1-\frac{4}{5})^2 = \frac{4}{5}(\frac{25}{5}+ \frac{4}{5})-(\frac{5}{5}-\frac{4}{5})^2 = \frac{4}{5} \cdot \frac{29}{5} - (\frac{1}{5})^2 = \frac{116}{25} - \frac{1}{25} = \frac{115}{25} = \frac{23}{5} = 4.6$$
Ответ: 4.6