[tex]cos^{4} \alpha - sin^{4} \alpha[/tex]
[tex]\alpha =30^{o}[/tex]
[tex]cos\ 30^{o} = \frac{\sqrt{3} }{2} \\sin\ 30^{o} = \frac{1}{2}[/tex]
[tex]cos^{4} \alpha - sin^{4} \alpha = (\frac{\sqrt{3} }{2} )^{4} - (\frac{1}{2}) ^{2} = \frac{9}{16} - \frac{1}{16} = \frac{8}{16} = \frac{1}{2}[/tex]
Odp. B
