IGCSEMathsCambridge (CIE)International MathsCoreRevision NotesGeometryBasic Angle PropertiesAngles in Triangles

Angles in Triangles (Cambridge (CIE) IGCSE International Maths)

Revision Note

Jamie Wood

Written by: Jamie Wood

Reviewed by: Dan Finlay

Angles in Triangles

What are the angle properties of triangles?

  • The three interior angles inside any triangle add up to 180°

  • If the triangle is isosceles then two angles will be equal

    • These will be the two angles opposite the two sides of equal length

  • If the triangle is equilateral then all three angles will be equal

    • Each angle will equal 60°

  • A right-angled triangle has one 90° angle

angle properties of triangles

Examiner Tips and Tricks

  • Find all the missing angles that you can using the angles that are given to you in a question

    • They might not seem to help you straight away but having more angles will lead you to find the angle you need

Worked Example

The diagram below is formed using three straight lines. Find the value of x.

Triangle angle properties worked example question

Label the other missing angles inside the triangle
 

Triangle angle properties worked example working

Vertically opposite angles between two intersecting lines are equal

y space equals space 60

Angles that meet on a straight line add up to 180°

table row cell z space plus space 130 space end cell equals cell space 180 space end cell row cell z space end cell equals cell space 50 end cell end table

Interior angles in a triangle add up to 180°

table row cell x plus 60 plus 50 end cell equals 180 row cell x plus 110 end cell equals 180 end table

bold italic x bold space bold equals bold space bold 70

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    Author
    Reviewer
    Jamie Wood

    Author: Jamie Wood

    Expertise: Maths

    Jamie graduated in 2014 from the University of Bristol with a degree in Electronic and Communications Engineering. He has worked as a teacher for 8 years, in secondary schools and in further education; teaching GCSE and A Level. He is passionate about helping students fulfil their potential through easy-to-use resources and high-quality questions and solutions.

    Dan Finlay

    Author: Dan Finlay

    Expertise: Maths Lead

    Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.