Đáp án: \(\left[ \begin{array}{l}x = \dfrac{125}{2} + k180^0\\x = -\dfrac{145}{2} + k180^0\end{array} \right.\) `(k ∈ ZZ)`
Giải thích các bước giải:
`cos (2x + 10^0) = -(\sqrt{2})/2`
`<=> cos (2x + 10^0) = cos 135^0`
`<=>` \(\left[ \begin{array}{l}2x + 10^0 = 135^0 + k360^0\\2x + 10^0 = -135^0 + k360^0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}2x = 125^0 + k360^0\\2x = -145^0 + k360^0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x = \dfrac{125}{2} + k180^0\\x = -\dfrac{145}{2} + k180^0\end{array} \right.\) `(k ∈ ZZ)`
