langkah nya bagaimana?

mis theta/2 = @
1-tan²(@°) / 1+tan²(@°)
1-sin²(@)/cos²(@) / 1+sin²(@)/cos²(@)
cos²(@)-sin²(@)/cos²(@) / cos²(@)+sin²(@)/cos²(@)
cos2(@)/1 = cos2(@)
= cos 2(theta/2)
= cos (theta)