Question

cos(30° + a) - cos(30-a)​

Answer 1

Ответ:

$cos(30^\circ +a)-cos(30^\circ -a)=\\\\=(\underline {cos30^\circ \cdot cosa}-sin30^\circ \cdot sina)-(\underline{cos30^\circ \cdot cosa}+sin30^\circ \cdot sina)=\\\\=-2\cdot sin30^\circ \cdot sina=-2\cdot \dfrac{1}{2}\cdot sina=-sina$

Answer 2

Ответ:

cos(30°+a)-cos(30°-a) = (cos × 30° × cos × a - sin × 30° × sin × a) - ( cos × 30° × cos × a + sin × 30° × sin × a) = -2 × sin × 30° × sin × a = -2 × 1/2 × sin × a = - sin × a.