Odpowiedzi

2009-11-08T20:07:22+01:00
(1 + sin x) * (1/cos x - 1/ctg x) - cos x =
(1 + sin x) * (1/cos x - tg x) - cos x =
(1 + sin x) * (1/cos x - sin x / cos x) - cos x =
(1 + sin x) * ( (1 - sin x)/cos x ) - cos x =
[(1 + sin x) * (1 - sin x)] / cos x - cos x =
(1 - sin² x)/cos x - cos x = (cos² x)/cos x - cos x = cos x - cos x = 0