Question

Нужна помощь.,.,.,.,.,.,.,.,.,......

Answer 1

$cos15аcos105а=cos15аcos(90а+15а)=cos15аsin15а= \ \ = dfrac{2cos15аsin15а}{2} = dfrac{sin30а}{2} = dfrac{ frac{1}{2} }{2} = dfrac{1}{4} =0.25$