Question

Спростіть вираз: 2cos18˚cos12˚ - cos6˚

Answer 1

$2cos18^\circ*cos12^\circ- cos6^\circ=$$2* \frac{1}{2} (cos(18^\circ-12^\circ)+cos(18^\circ+12^\circ))-cos6^\circ=$$cos6^\circ+cos30^\circ-cos6^\circ=cos30^\circ= \frac{ \sqrt{3} }{2}$