This study notes covers Common Mistakes within Properties of Triangles for GCSE Mathematics. Revise Properties of Triangles in Geometry & Measures for GCSE Mathematics with 12 exam-style questions and 3 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 7 of 9 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
Common Mistakes
✗ Wrong: Assuming all isosceles triangles have angles of 45°, 45°, 90°
✓ Right: Isosceles just means 2 equal sides/angles - the actual angles vary
✗ Wrong: Exterior angle = 180° − interior angle at same vertex
✓ Right: That IS true, but the quicker method is: exterior = sum of OTHER two interior angles
Practice questions for Properties of Triangles
What is the sum of the interior angles of any triangle?
Describe the key properties of an equilateral triangle. State two properties relating to sides and two relating to angles.
Quick recall flashcards
Triangle Angle Sum
Always 180°
Isosceles Triangle
Two equal sides, two equal angles