Ответы и объяснения

2013-12-29T15:17:24+04:00
2013-12-29T15:21:04+04:00
 (1+ 1/ctg²(π/2 - α) ) * sin²α = (1+tg²(π/2 - α)) * sin²α = (1+ctg²α) * sin²α = 1/sin²α * sin²α = 1