Question

Sa se calculeze cos8x stiind ca tgx*tg2x=ctg2x*ctg3x

Answer 1

Răspuns:

Explicație pas cu pas:

$cos8x=cos(8*\frac{4\pi }{3})=cos\frac{32\pi }{3} =cos(\frac{30\pi+2\pi}{3} )=cos(10\pi+\frac{2\pi }{3})==cos(5*2\pi+\frac{2\pi }{3})=cos(\frac{2\pi }{3})=cos(\pi-\frac{\pi}{3} )=-cos \frac{\pi}{3}=-\frac{1}{2}$