Question

Дано: sinα=  -8|17 ; π<α>3π|2

Вычислите:    1)cos2α

                          2) Ctg (π|2 +α) 

Answer 1

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