Tìm k

$$\begin{gathered} \mathrm{Cho} \mathrm{Parabol} \left(\mathrm{P}\right) \mathrm{y}=-2{\mathrm{x}}^2 \\ \mathrm{a}) \mathrm{Tìm} \mathrm{k} \mathrm{để} \mathrm{đường} \mathrm{thẳng} (\mathrm{d}) \mathrm{y}=\mathrm{kx} + 2 \mathrm{tiếp} \mathrm{xúc} (\mathrm{P}\left) \\ \mathrm{b}\right) \mathrm{Chứng} \mathrm{minh} \mathrm{điểm} \mathrm{E}(\mathrm{m};{\mathrm{m}}^2+1) \mathrm{không} \mathrm{thuộc} \mathrm{P} \mathrm{với} \mathrm{mọi} \mathrm{giá} \mathrm{trị} \mathrm{của} \mathrm{m} \end{gathered}$$