alleryThe equation of a plane in normal form (with unit normal n̂ and perpendicular distance d from origin) is
Ar · n̂ = d
Br × n̂ = d
Cr + n̂ = d
Dr / n̂ = d
Answer & Solution
Correct answer: A. r · n̂ = d
1. In normal form, n̂ is a unit normal vector and d is the perpendicular distance from the origin.
2. For any point r on the plane, its projection on n̂ equals d.
3. The projection is the dot product r · n̂.
4. So the plane equation is r · n̂ = d.
_Source: syllabus Maths Part 2 Ch 11 "Three Dimensional Geometry", §11.6.1_
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