cos ²x + cosx= 0 ( π/2
cos ²x + cosx= 0 ( π/2
By Reese
By Reese
Ptrinh tương đương vs
$$\cos x(\cos x + 1) = 0$$
Vậy $\cos x = 0$ hoặc $\cos x = -1$ hay $x = 2k\pi$ hoặc $x = (2k+1) \pi$.
Do $x \in (\dfrac{\pi}{2}, \dfrac{3\pi}{2})$ nên
$$x = \pi$$