Question

3 cos 300° - 2 cos 225° + cos 120°

Answer 1

3 cos 300º = $3 * \frac{1}{2}$
2 cos 225º = $2 * \frac{ \sqrt{} 2}{2}$
cos 120º = $\frac{1}{2}$

Assim, temos que:

$3 * \frac{1}{2} - 2 * \frac{ \sqrt{2} }{2} + \frac{1}{2} \\ \frac{3}{2} - 2 * \frac{ \sqrt{2} }{2} + \frac{1}{2}$

Faz MMC 2 = 2 
Portanto:

$\frac{3 - 2 \sqrt{2}+1 }{2} \\ \frac{4 - 2 \sqrt{2} }{2} \\ 2 - \sqrt{2}$