Преобразуйте в произведение: 1) cos 7x - cos 17x 2) Корень 11 sin 3a + 2cos 3a

[latex]1)\; \; cos7x-cos17x=-2\cdot sin\frac{7x-17x}{2}\cdot sin\frac{7x+17x}{2}=2\cdot sin5x\cdot sin12x\\\\2)\quad \sqrt{11}sin3a+2cos3a=[\; (\sqrt{11})^2+2^2=11+4=15\; ]=\\\\=\sqrt{15}\cdot \left (\frac{\sqrt{11}}{\sqrt{15}}\cdot sin3a+\frac{2}{\sqrt{15}}\cdot cos3a\right )=\\\\=\Big [\; tak\; kak\; \left (\frac{\sqrt{11}}{\sqrt{15}}\right )^2+\left (\frac{2}{\sqrt{15}}\right )^2=1,\; to \; \frac{\sqrt{11}}{\sqrt{15}}=cos \beta ,\; \frac{2}{\sqrt{15}}=sin\beta \; \Big ]=\\\\=\sqrt{15}\cdot \Big (cos \beta \cdot sin3a+sin \beta \cdot cos3a\Big )=\sqrt{15}\cdot sin(3a+ \beta ),\; \; tg\beta =\frac{2}{\sqrt{11}}[/latex]