240 GEOMETRY •^ ANGLES INSIDE TRIANGLES
Strong shapes
Triangles are useful shapes for
engineers as they are stable
and hard to pull out of shape.
This geodesic dome is made
from triangular panels, which
work together to carry weight
evenly. This makes the
structure light, but very strong.
REAL WORLD MATHS
Angles inside triangles
triangles
We give names to triangles according to the lengths
of their sides and the sizes of their angles. We
learned about the sides of a triangle on page 214,
so now let's have a closer look at its angles.
60º 60º
60º
The two angles that
are not right angles can
be the same or different
Equal sides are
marked with a dash
Equilateral triangle
An equilateral triangle is the more
usual name for a regular triangle. Its three
angles are all 60°. Its three sides are
always the same length, too.
Right-angled triangle
A right-angled triangle contains one right
angle, which is exactly 90°. The other two angles
can be the same, or different, like this one. It can
have two sides of the same length, or all three can
be different.
Types of triangles
Here are the triangles we see
most often in geometry.
Equal angles
are marked
with arcs
There are four kinds of
triangle: equilateral,
right-angled, isosceles,
and scalene.
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