Geometry Constructions
Construct triangles and angles using a compass
Geometry Constructions
In geometry, constructions are accurate drawings made using specific tools: a ruler (straight edge), a compass, and a protractor. We construct lines, angles, and shapes by following precise steps.
Constructing Angles
To construct an angle with a protractor: 1) Draw a base line with a ruler. 2) Place the protractor's centre on the endpoint. 3) Line up the base line with 0°. 4) Mark the required angle. 5) Remove the protractor and draw the second line through the mark.
Example
Constructing Triangles
Construct a triangle with sides 5 cm, 4 cm, and 3 cm:
Step 1: Draw the base line = 5 cm.
Step 2: Set compass to 4 cm, draw an arc from one end.
Step 3: Set compass to 3 cm, draw an arc from the other end.
Step 4: Where the arcs cross is the third point.
Step 5: Connect all three points.
Example
Bisecting a Line Segment
To find the exact middle of a line AB:
Step 1: Set compass to more than half of AB.
Step 2: Draw arcs from A above and below the line.
Step 3: Draw arcs from B above and below (same radius).
Step 4: The arcs intersect at two points. Connect them — this line crosses AB at its midpoint.
Note
Remember
Always use a sharp pencil for accuracy. Keep your compass setting steady when drawing arcs. Label all points, lines, and angles clearly. Double-check measurements before drawing.
Key Vocabulary
ConstructTo draw accurately using tools
CompassA tool for drawing circles and arcs
ProtractorA tool for measuring and drawing angles
BisectTo divide exactly in half
ArcPart of a circle drawn with a compass
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