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Two planes a₁x + b₁y + c₁z = d₁ and a₂x + b₂y + c₂z = d₂ are perpendicular iff
Aa₁/a₂ = b₁/b₂ = c₁/c₂
Bd₁ = d₂
Ca₁a₂ + b₁b₂ + c₁c₂ = 0
Da₁ = a₂
Answer & Solution
Correct answer: C. a₁a₂ + b₁b₂ + c₁c₂ = 0
1. Each plane has a normal vector (a, b, c).
2. Planes are perpendicular iff their normals are perpendicular.
3. Normals are perpendicular iff their dot product is zero, i.e. a₁a₂+b₁b₂+c₁c₂=0.
_Source: Maharashtra Balbharati Std XII Mathematics Part 1, Ch 6 "Line and Plane" §6.6_
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