Angle Between Two Planes (cos θ = |n1·n2|/(|n1||n2|) for acute angle between planes)

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cos θ = |n1·n2|/(|n1||n2|) for acute angle between planes

What each symbol means

SymbolWhat it stands for
n1,n2Normals to the planes

When to use this

Acute angle convention: use absolute value on dot product.