alleryThe angle θ between two PLANES with normals n1 and n2 satisfies:
A$\cos \theta = (n_1 · n_2)/(|n_1||n_2|)$
B$\sin \theta = (n_1 · n_2)/(|n_1||n_2|)$
C$\tan \theta = |n_1 × n_2|/|n_1 · n_2|$
D$\theta = n_1 + n_2$
Answer & Solution
Correct answer: A. $\cos \theta = (n_1 · n_2)/(|n_1||n_2|)$
Angle between two planes = angle between their normals: cos θ = (n1 · n2)/(|n1||n2|).
For line-plane angle, it's sin θ (complement).
For two lines, it's cos θ between direction vectors.
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