toan11-khác cos2x#cosx

C

chauhien93

Chỉ có tính chất tham khảo
[TEX]cos2x\neq cosx[/TEX]
[TEX]\Leftrightarrow cos2x-cosx \neq 0[/TEX]
[TEX]\Leftrightarrow 2cos^2 x-cosx -1\neq 0[/TEX]
[TEX]\Leftrightarrow \left\{ \begin{array}{l} cosx\neq 1 \\ cosx \neq \frac{-1}{2} \end{array} \right.[/TEX]
[TEX].....................\Leftrightarrow Xong [/TEX]
 
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