Question

Помогите решить,вообще не пойму

Answer 1

$1)\quad \frac{cos43\cdot cos17-sin43\cdot sin17}{sin37\cdot cos23+cos37\cdot sin23} =\frac{cos(43+17)}{sin(37+23)} =\frac{cos60}{sin60} =ctg60=\frac{\sqrt3}{3}\\\\2)\quad 2\, sin15\cdot cos15=sin30=\frac{1}{2}\\\\3)\quad cos^2\frac{\pi}{8}-sin^2\frac{\pi}{8}=cos(\frac{2\pi}{8})=cos \frac{\pi}{4} =\frac{\sqrt2}{2}$