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Angle θ between two planes 2x + 3y + 4z = 0 and x + y + z = 0:
Acos θ = 9/sqrt(29 × 3) = 9/sqrt(87)
B90°
C45°
D0
Answer & Solution
Correct answer: A. cos θ = 9/sqrt(29 × 3) = 9/sqrt(87)
Normals: (2,3,4) and (1,1,1). cos θ = (2+3+4)/sqrt(4+9+16)sqrt(1+1+1) = 9/sqrt(29)sqrt(3) = 9/sqrt(87) ≈ 0.965. θ ≈ 15.2°.
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