Constructions, nets and solids
Constructions and scale drawings
- To construct a triangle from three sides: draw the base with a ruler, then use compasses to swing an arc for each other side. Leave the arcs showing.
- A scale drawing shows a real object by a fixed scale, such as $1\ \text{cm}$ to $5\ \text{m}$.
Practice
To construct a triangle from three given sides you mainly use a ruler and:
Compasses swing arcs of the correct length for the other two sides.
Nets and solids
- A net is a flat shape that folds into a solid — handy for surface area.
- A flat side of a solid is a face, two faces meet at an edge, and corners are vertices.
Practice
A flat shape that folds up into a solid is called a ______.
A net is the unfolded, flat version of a solid.
Naming solids
- cube / cuboid (box shapes), prism (same shape all along), cylinder (a circular prism).
- pyramid / cone (come to a point), sphere / hemisphere (a ball / half a ball).
- A cube has $6$ faces, $12$ edges and $8$ vertices.
Practice
How many faces does a cube have?
A cube has 6 square faces (12 edges, 8 vertices).
You've got it
Key idea
- construct with ruler + compasses; leave the construction arcs
- a net folds into a solid (good for surface area)
- a cube: $6$ faces, $12$ edges, $8$ vertices