1) 1/(1 + cos a) + 1/(1 - cos a) = (1 + 1 - cos a + 1 + cos a) / (1 - cos^2 a) = 2 / sin^2 a 2) ctg(2B)(cos(2B) - 1) + 1 = ctg(2B)(cos^2(2B) - sin^2(2B)) + 1 = ctg(2B)cos(4B) + 1 3) (tgB + 1) / (1 + ctgB) = (sin B / cos B + 1) / (1 + cos B / sin B) = (sin^2 B + cos B) / (cos B + sin B) = (1 + cos B) / 1 = 1 + cos B
1) 1/(1 + cos a) + 1/(1 - cos a) = (1 + 1 - cos a + 1 + cos a) / (1 - cos^2 a) = 2 / sin^2 a
2) ctg(2B)(cos(2B) - 1) + 1 = ctg(2B)(cos^2(2B) - sin^2(2B)) + 1 = ctg(2B)cos(4B) + 1
3) (tgB + 1) / (1 + ctgB) = (sin B / cos B + 1) / (1 + cos B / sin B) = (sin^2 B + cos B) / (cos B + sin B) = (1 + cos B) / 1 = 1 + cos B