Answer: arccos(1/3).
- A arccos(1/3)
- B arccos(2/3)
- C 60°
- D 90°
Correct answer: A. arccos(1/3)
Explanation: cosθ = (1·1 + 1·(−1) + 1·1)/(√3·√3) = 1/3, so the angle is arccos(1/3).
Three mutually perpendicular axes x, y, z meeting at the origin O, with a point P located by its (x, y, z) coordinates.
Concept context
Lines and planes in 3D space, direction cosines, distances, and angles