Question

Обчисліть: 4 cos45° cos15°

Answer 1

Ответ:

$4\, cos45^\circ \ cos15^\circ =sin90^\circ =\dfrac{1}{2}\cdot (cos60^\circ +cos30^\circ )=\dfrac{1}{2}\cdot \Big(\dfrac{1}{2}+\dfrac{\sqrt3}{2}\Big)=\\\\=\dfrac{1+\sqrt3}{4}$