2cos(pi-альфа)+(sin альфа+tg альфа)^2-cos^2 альфа

$2cos( \pi -a) + (sin(a) +tg(a))^2 - cos^2(a) -2cos(a) + sin^2(a) + \frac{2sin^2(a)}{cos(a)} + tg^2(a) - cos^2(a) sin^2(a) - cos^2(a) + \frac{2sin^2(a)}{cos(a)} - 2cos(a) + tg^2(a)$
$sin^2(a) - cos^2(a) + \frac{2sin^2(a) -2cos^2(a)}{cos^2(a)} + tg^2(a)$
$-cos(2a) + \frac{-2cos(2a)}{cos^2(a)} + tg^2(a)$
$-cos(2a) + -2cos2a \frac{1}{cos^2(a)} + tg^2(a) -cos(2a) -2cos(2a)(1+tg^2(a)) + tg^2(a) -3cos(2a) - cos(2a)tg^2(a) + tg^2(a)$

ответ:
$-3cos(2a) - tg^2(a)(cos(2a) - 1)$