OpenOlympiad
Concept 4 of 10Foundation
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Perpendicular from a point

Drop a perpendicular from a point P to a line ℓ:

  1. From P, draw an arc cutting ℓ at two points X, Y.
  2. From X and Y (same radius, bigger than XY/2), draw arcs meeting at Q (opposite side of P).
  3. Line PQ is perpendicular to ℓ.

Shortcut: use a set square's right-angle edge.

Example
Find the height of a triangle: drop a perpendicular from the top vertex to the base.
💡 Tip:Perpendicular = SHORTEST distance from a point to a line.
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5 questions to check what you just read.

0 / 5
  1. Q1.Shortest distance from a point to a line is:
  2. Q2.A set square's right-angle edge is useful for drawing:
  3. Q3.Perpendicular from a point P to line ℓ can be constructed using:
  4. Q4.If line ℓ is horizontal, the perpendicular from a point above ℓ is:
  5. Q5.Altitude in a triangle is: