Angles in triangles · Year 7
In Year 7 you learn: isosceles and equilateral triangles.
The three angles inside any triangle always add up to 180°. Combined with facts about isosceles and equilateral triangles, this lets you find any missing angle, and the exterior-angle rule gives a useful shortcut.
Key facts
- Angles in a triangle add up to 180°.
- In an isosceles triangle the two base angles (opposite the equal sides) are equal.
- In an equilateral triangle every angle is 60°.
- In a right-angled triangle the other two angles add up to 90°.
Worked examples
Example 1
Why do the angles in any triangle add up to 180°?
Answer: They fit together on a straight line, and angles on a straight line add up to 180°.
Example 2
Find the angle x.
Answer: x = 60°
Example 3
This triangle is isosceles. The top angle is 40°. Find each base angle y.
Answer: y = 70°