`a)` Bạn viết lại đề !!!
`b) cos 2x + sin x + 1 = 0`
`<=> 1 - 2sin² x + sin x + 1 = 0`
`<=> -2sin² x + sin x + 2 = 0`
`<=>` \(\left[ \begin{array}{l}x = arcsin \dfrac{1 + \sqrt{17}}{4} + k2π\\x = π - arcsin \dfrac{1 +\sqrt{17}}{4} + k2π\\x = arcsin \dfrac{1 - \sqrt{17}}{4} + k2π\\x = π - arcsin \dfrac{1 - \sqrt{17}}{4} + k2π\end{array} \right.\) `(k ∈ ZZ)`
`c) ĐK: x ne k(π)/2`
`PT`
`=> tan x - 2.(1)/(tan x) + 1 = 0`
`<=> tan² x - 2 + tan x = 0`
`<=>` \(\left[ \begin{array}{l}tan x = 1\\tan x = -2\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x = \dfrac{π}{4} + kπ\\x = arctan (-2) + kπ\end{array} \right.\) `(k ∈ ZZ)`
