Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 2 - No. 17)
If cos(θ) = -0.5 and θ is in the second quadrant, then θ is approximately:
30°
60°
120°
150°
Explanation
arccos(0.5) = 60°, then θ = 180 - 60 = 120°
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