Angles in triangles · Grade 7

In Grade 7 you learn: angles in a triangle add to 180°; 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

This triangle is isosceles. The top angle is 40°. Find each base angle y.

Answer: y = 70°

Other years