Primary 5 Triangles
Keywords
- Isosceles
- Two equal sides and two equal base angles.
- Equilateral
- Three equal sides and three 60° angles.
- Right-angled
- One angle is 90°.
- Angle sum
- The three inside angles of a triangle add up to 180°.
Properties of triangles
Choose a triangle. Watch the markings appear to see what its sides and angles tell us.
Explore a triangle
Its top angle is 40°. What are the two base angles?
Step 0 of 3
Try together
An isosceles triangle has a top angle of 50°. Find each base angle.
Reveal the answer
180° − 50° = 130°. Each equal base angle is 130° ÷ 2 = 65°.
Angle sum of a triangle
The three inside angles of a triangle add up to 180°.
Find the missing angle
Two angles are 50° and 60°. What is angle x?
Reveal the answer
50° + 60° = 110°.
x = 180° − 110° = 70°.
Try together
A triangle has angles of 45° and 65°. Find its third angle.
Reveal the answer
45° + 65° = 110°. The third angle is 180° − 110° = 70°.