16.11. (sin a - cos a)^2 = p^2
sin^2 a - 2sin a*cos a + cps^2 a = 1 - sin 2a = p^2
sin 2a = 1 - p^2
16.12. 2 - 13cos 2a + sin^(-1) (2a) = 2 - 13cos 2a + 1/sin 2a
ctg a = -1/5, значит, tg a = 1/ctg a = -5.
cos 2a = (1 - tg^2 a) / (1 + tg^2 a) = (1 - 25) / (1 + 25) = -24/26 = -12/13
sin 2a = 2tg a / (1 + tg^2 a) = 2(-5) / (1 + 25) = -10/26 = -5/13
2 - 13cos 2a + 1/sin 2a = 2 - 13(-12/13) + (-13/5) = 2 + 12 - 2,6 = 11,4