Question

100 баллов!!
#15 1,2

Answer 1

/////////////////////1) 1/cos^2a

Answer 2

Jib,rf/

Answer 3

Ошибка, минус на минус даёт плюс!

Answer 4

точно

Answer 5

sin² a + cos² a =1
tg a = sin a /cos a
sec a = 1/cos a 
1/
tg(a) - (sin(a) - 1)/cos(a) = sin(a)/cos(a) - (sin(a) - 1)/cos(a) = (sin(a) - sin(a) + 1)/cos(a) = 1/cos(a) = sec(a) (секанс)
2.
(1 + cos(a))/sin(a) * (1-cos(a))/sin(a) =  (1 - cos² (a))/sin² (a) = sin² (a)/sin² (a) = 1