[mercedesbenz]

$$\cos(15)=\cos(45-30)=\cos 45\cos 30 + \sin 45\sin 30 =\frac{\sqrt{2}}{2}\frac{\sqrt{3}}{2}+\frac{\sqrt{2}}{2}\frac{1}{2}=\frac{\sqrt{6}}{4}+\frac{\sqrt{2}}{4}=\frac{\sqrt{6}+\sqrt{2 }}{4}$$
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