[tex]\displaystyle\bf\\\frac{\sqrt{3} }{2} +Cos\alpha =Cos30^\circ+Cos\alpha =2Cos\frac{30^\circ+\alpha }{2} Cos\frac{30^\circ-\alpha }{2} =\\\\\\=2Cos\Big(15^\circ+\frac{\alpha }{2} \Big)\cdot Cos\Big(15^\circ-\frac{\alpha }{2} \Big)[/tex]