Question

Valoarea numărului cos 75 °este:
$a) \frac{ \sqrt{6}+ \sqrt{2} }{4} b) \frac{ \sqrt{2} - \sqrt{6} }{4}c) \frac{ \sqrt{6}- \sqrt{4} }{4} d)\frac{ \sqrt{6}- \sqrt{2} }{2}$
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Answer 1

[tex]\cos75\textdegree=\cos(30\textdegree+45\textdegree)=\cos30\textdegree\cos45\textdegree-\sin30\textdegree\sin45\textdegree=\\ ~~~~~~~~~~=\frac{\sqrt3}{2}\frac{\sqrt2}{2}-\frac{1}{2}\frac{\sqrt2}{2}=\frac{\sqrt6-\sqrt2}{4}[/tex]
Deci niciuna dintre valori nu e corecta. Daca nu crezi, verifica si alte surse.