[tex]Metoda$ $\boxed{1}:\\\\ cos130^o+ cos50^o = 2\cdot cos\frac{130+50}2}\cdot cos\frac{130-50}2} = \\ =2\cdot cos 90\cdot cos40 = 2\cdot 0\cdot cos40 = 0 \\ \\ \\
Metoda$\boxed{2}:\\\\ cos130^o + cos50^o = \\ = cos(180^o-50^o) + cos50^o = -cos50^o + cos50^o = 0[/tex]
