Respuesta :

bappyisc

Answer:

-90 , 30

Step-by-step explanation:

sina = cos(2a)

       = 1 - 2(sina)^2

2(sina)^2 + sina -- 1 = 0

( sina + 1 )( 2sina - 1 ) = 0

sina = -1                     or sina = 1/2

=> a = -90 degrees   or => a = 30 degrees