Bonjour laur1a5SarabJ0uliajo
[tex]\cos^2x = \cos^2\dfrac{\pi}{7}\\\\\cos x = \cos\dfrac{\pi}{7}\ \ ou\ \ \cos x = -\cos\dfrac{\pi}{7}\\\\\cos x = \cos\dfrac{\pi}{7}\ \ ou\ \ \cos x = \cos(\pi-\dfrac{\pi}{7})\\\\\cos x = \cos\dfrac{\pi}{7}\ \ ou\ \ \cos x = \cos\dfrac{6\pi}{7}\\\\Dans\ ]-\pi;\pi],\\\\\ \boxed{x=\dfrac{\pi}{7}\ \ ou\ \ x=-\dfrac{\pi}{7}\ \ ou\ \ x=\dfrac{6\pi}{7}\ \ ou\ \ x=-\dfrac{6\pi}{7}}[/tex]
