diketahui luas permukaan kubus 864 cm2. perbandingan rusuk kubus dan p balok 3 : 4 perbandingan p l dan tinggi 4:3:2 luas permuk
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The basic angle for 1/2 is 60°, and cosines are negative in the first and third quadrant.
So, you take 180° - 60° = 120° to get the angle in the first quadrant, and 180° + 60° = 240° to get the angle in the third quadrant.
Since only 120° is an option, the answer is B.