Найдите множество решений неравенства: (2x+1)(x-4)<=5.

\[(2x + 1)(x - 4) \leq 5\]

\[2x^{2} - 8x + x - 4 - 5 \leq 0\]

\[2x² - 7x - 9 \leq 0\]

\[D = 49 + 72 = 121\]

\[x_{1} = \frac{7 + 11}{4} = 4,5\]

\[x_{2} = \frac{7 - 11}{4} = - 1\]

\[Ответ:\lbrack - 1;4,5\rbrack.\]