How_To_Be_Good_At_Math

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.

240_241_Angles_inside_triangles.indd 240 29/02/2016 18:05