Дано: sinα= -8|17; π3π|2 вычислите: 1)cos2α 2) ctg (π|2 +α)

1) соs 2a = 1 - 2sin^2 a = 1- 2(-8/17)^2 = 161/289

2) Ctg (π|2 +α) = - tg a

tg a = sin a / cos a

cos a = - корень (1-(-8/17)^2)=-15/17

tg a =  (-8/17)/( -15/17 )=8/15

 Ctg (π|2 +α) = -8/15