A perpendicular bisection of a straight line is a geometric construct intended to create a 90° angle using a compass.
Method
- Draw the line to be bisected
- Draw the centre circle
- Draw second circle
- Draw third circle
- Bisect line
Draw Line To Be Bisected
The bisection will be of a straight line a-b. The length of this line is unimportant and is used simply for explaining the construct. The line should be drawn using a ruler.
Drawing Centre Circle
Around the middle of line a-b, circle c is drawn. Radius x is of no particular size, but making the diameter of the circle approximately ⅓ of the length of line a-b makes the bisection easier to construct.
Drawing Second Circle
Where circle c intersects line a-b, place the point of the compass and draw a second circle d with a radius y larger than that of circle c.
Draw Third Circle
On the opposite side of circle c where it intersects line a-b, place the point of the compass and draw a third circle with the same radius y as circle d.
Bisect Line
Draw a straight line using a ruler that touches the intersecting points of circles d and e. The bisection of line a-b by line f-g will be at 90°.
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