kerjain nomor 26 dong kak

π = 180°
cos^2(2/3π) - sin^2(2/3π)
cos^2(2/3 × 180°) - sin^2(2/3 × 180°)
cos^2(120°) - sin^2(120°)
- cos^2(180° - 60°) - sin^2(180° - 60°)
- cos^2 60° - sin^2 60°
(-1/2)^2 - (1/2√3)^2
1/4 - 3/4 = -1/2
Jawabannya B (-1/2)