Find the unknown angle in triangles and quadrilaterals

Key Notes :

🔮 The sum of the angles in a quadrilateral is always 360°.

🔮 The sum of the angles in a triangle is always 180°.

Learn with an example

✈️ What is the measure of the missing angle?

  • The sum of the four angles must be 360°. The three angles you know measure 39°, 116°, and 64°.
  • Write an equation and find the measure of the unknown angle.
  • 39° +116° + 64° + ? = 360°
  • 219° + ? = 360°
  • ? = 360° − 219°
  • ? = 141°
  • The measure of the missing angle is 141°.

✈️ What is the measure of the missing angle?

  • The sum of the three angles must be 180°. The two angles you know measure 90° and 36°.
  • Write an equation and find the measure of the unknown angle.
  • 90° +36° + ? = 180°
  • 126° + ? = 180°
  • ? = 180° − 126°
  • ? = 54°
  • The measure of the missing angle is 54°.

✈️ What is the measure of the missing angle?

  • The sum of the four angles must be 360°. The three angles you know measure 150°, 60°, and 56°.
  • Write an equation and find the measure of the unknown angle.
  • 150° + 60° + 56° + ? = 360°
  • 266° + ? = 360°
  • ? = 360° − 266°
  • ? = 94°
  • The measure of the missing angle is 94°.

Let’s practice!🖊️