G S Rehill's Interactive Maths Software Series - "Building a Strong Foundation in Mathematics" from mathsteacher.com.au.

Order a 12-month Year 7 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 8 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 9 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 10 Interactive Maths software Homework Licence for only $19.95.

Year 8 Interactive Maths - Second Edition


Triangles

A plane is a flat or level surface in two dimensions.  Figures such as circles or squares have all of their parts lying on a plane and thus, are examples of plane figures.


A triangle is a closed plane figure bounded by three line segments.


Types of Triangles

Triangles can be classified according to the length of their sides and the size of their angles.


Classifying Triangles according to the Length of their Sides

Scalene Triangles

A scalene triangle has no equal sides.


Equilateral Triangles

An equilateral triangle has all sides equal.

All angles of an equilateral triangle are 60.


Note:
  • To show that the sides of an equilateral triangle have the same length, we place identical marks on the sides of the triangle.
  • To show that the angles of an equilateral triangle are equal in size, we place identical curves on each angle.

Isosceles Triangles

An isosceles triangle has two sides equal.

The angles opposite the equal sides are equal.


Note:
  • In the diagram, side BC has a different length to AB and AC.
  • The side of the isosceles triangle that has a different length is said to be the base of the triangle.  So, BC is the base.
  • Identical marks on the sides indicate that the sides are equal.
  • Identical marks on the angles indicate that the angles are equal.


Example 8

Classify each of the following triangles according to the lengths of their sides:

Solution:


Classifying Triangles according to the Size of their Angles

Acute-angled Triangles

An acute-angled triangle has all angles less than 90 (i.e. all three angles are acute).


Obtuse-angled Triangles

An obtuse-angled triangle has one angle greater than 90.  That is, one angle is obtuse.


Right-angled Triangles

A right-angled triangle has one angle equal to 90.  That is, one angle is a right angle.


Note:
  • The side opposite the right angle is called the hypotenuse.
  • The hypotenuse is the longest side of the triangle (which can be verified with a ruler).


Example 9

Classify each of the following triangles according to the size of their angles

Solution:


Activity 9.1


Key Terms

plane, plane figure, triangle, vertex of a triangle, scalene triangle, equilateral triangle, isosceles triangle, acute-angled triangle, obtuse-angled triangle, right-angled triangle, hypotenuse


| Home Page | Order Maths Software | About the Series | Maths Software Tutorials |
| Year 7 Maths Software | Year 8 Maths Software | Year 9 Maths Software | Year 10 Maths Software |
| Homework Software | Tutor Software | Maths Software Platform | Trial Maths Software |
| Feedback | About mathsteacher.com.au | Terms and Conditions | Our Policies | Links | Contact |

Copyright 2000-2019 mathsteacher.com Pty Ltd.  All rights reserved.
Australian Business Number 53 056 217 611

Copyright instructions for educational institutions

Please read the Terms and Conditions of Use of this Website and our Privacy and Other Policies.
If you experience difficulties when using this Website, tell us through the feedback form or by phoning the contact telephone number.