Réponses

2013-04-07T21:08:55+02:00

Bonsoir,

 

On sait que, quel que soit x, on a :

\cos ^2x + \sin ^2x = 1

Donc, on a :

\sin^2 x = 1-\cos ^2x\\ \sin x = \sqrt{1-\cos^2x}\\ \sin x = \sqrt{1-\left(\frac 12\right) ^2}\\ \sin x = \sqrt{1-\frac 14} = \sqrt{\frac 34} = \frac{\sqrt 3}{2}