Question

sin альфа=-4/5. Найдите 25cos2альф

Answer 1

1)cos2x = cos²x - sin²x
cos²x = 1 - sin²x
cos²x = 1 - 16/25cos²x = 9/25
2)cos2x = 9/25 - 16/25
cos2x = -7/25

Answer 2

cos2x=cosx^2-sinx^2=1-2*sinx^2=  1-32/25= -7/25
25cos2x= -7