Properties of Triangles Exercises for 11+ Maths
21 October 2026
Understanding triangle properties
Triangles are a key part of the 11+ Maths syllabus. Knowing how to spot and use their properties helps children solve a wide range of questions with confidence.
Key facts to remember
The three angles in any triangle always add up to 180 degrees. Triangles can be classified by their sides (equilateral, isosceles, scalene) or by their angles (acute, right, obtuse). The longest side is always opposite the largest angle.
Worked example
Let's look at a triangle with sides of 5 cm, 5 cm, and 8 cm.
First, notice that two sides are equal. This means the triangle is isosceles.
In an isosceles triangle, the angles opposite the equal sides are also equal.
Suppose the angle between the two equal sides is 40 degrees. The other two angles must be the same.
Add the known angle: 40 degrees.
Subtract from 180: 180 - 40 = 140 degrees left for the other two angles.
Divide by 2: 140 ÷ 2 = 70 degrees for each of the remaining angles.
The correct answer is that the triangle has angles of 40, 70, and 70 degrees.
Key insight: Encourage your child to check whether a triangle is equilateral, isosceles, or scalene before solving. This often makes finding missing angles or sides much easier.
Practice ideas
Ask your child to draw different types of triangles and label their side lengths and angles. Try giving one angle and two sides, then work out the missing angles together.
Building confidence
Regular practice with triangle properties helps children spot patterns and solve problems more quickly in the exam. Use simple examples and talk through each step.
