Brainlag PlusThe ruler-and-compass constructions, what each one gives, and when a triangle can be drawn at all.
The constructions
With a ruler (straight edge) and compasses only:
- Perpendicular bisector of AB: equal arcs from A and from B cross above and below; join the crossings. Every point on it is the same distance from A and B.
- Angle bisector: an arc from the vertex cuts both arms; equal arcs from those points cross; join to the vertex.
- Perpendicular from a point to a line, and a 60° angle from an equilateral triangle. Bisecting gives 30°, 45° and 15°.
Leave the construction arcs showing: on a paper they earn the marks.
The rest of this lesson and its 7 practice questions are in Plus.
Screen 1 of 3, free to read.
- 7 exam-style questions, marked as you go, each with a worked solution
- The Graphing Calculator beside every question
- Anything you get wrong is saved to your flashcards