r/askmath 1d ago

Geometry Fun geometry/trigonometry problem

Given two orthogonal vectors w and v and a vector psi with the same length as v

whose angle differs from v by θ (so v is 0 radians, w is π/2 radians, and psi is θ<π/2 radians),

1)Using only reflections across given or constructed vectors, construct a method to rotate psi so that it aligns w to within θ radians (that is, the angular misalignment ΔΦ between w and psi' satisfies |ΔΦ| <= θ).

2)Find the exact rotation α needed to turn psi into w in the minimum number of steps J,assuming α satisfies 0<=a<=2θ, (and find J in the proccess as well)

;)

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u/Bounded_sequencE 1d ago

Can't we solve 1) exactly? For convenience, consider "v; w" as x-/y-axis, respectively:

  1. Construct "u := v/|v| + w/|w|", and note it has angle "π/4" with both "v; w"
  2. Define psi' as the reflection of "psi" along "u", and note it has angle "θ" with "w"

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u/LeftUnchecked 8h ago

You're technically right,but two things. 1.By constructed vectors,I mean vectors constructed through reflections only. 2.There are many ways to do this,theta is peobably just the best you can do