An isosceles triangle has a top angle of 40°. Find the two base angles.
Step 1 Set up the equation
Let each base angle = x
40° + x + x = 180°
40° + 2x = 180°
Step 2 Solve for x
2x = 180° − 40° = 140°
x = 70°
Each base angle = 70°
This study notes covers Worked Example 2: Isosceles Triangle 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 5 of 9 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.
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.