Question

докажите тождество (cosa+sina)2-`1/ctg-sina*cosa=2tg2a

Answer 1

$2(cosalpha+sinalpha)-frac{1}{ctgalpha}-sinalpha*cosalpha=2tg2alpha;$
$2cosalpha+2sinalpha -frac{sinalpha}{cosalpha}-sinalpha*cosalpha=$
$=2tg2 alpha ;$