Geometry and measuresKey Stage 3

Sum of interior angles of a polygon

Use polygon angle facts to find missing values.

  • An -sided polygon splits into triangles.
  • Interior-angle sum: .

Example 1

Find the sum of the interior angles of this 5-sided polygon.

An -sided polygon can be split into triangles.

Example 2

Find the sum of the interior angles of this 6-sided polygon.

An -sided polygon can be split into triangles.

Your turn

Question 1

Find the sum of the interior angles of this 8-sided polygon.

Check answer
An -sided polygon can be split into triangles.
Question 2

Find the sum of the interior angles of this 9-sided polygon.

Check answer
An -sided polygon can be split into triangles.
Question 3

Find the sum of the interior angles of this 10-sided polygon.

Check answer
An -sided polygon can be split into triangles.
Question 4

Find the sum of the interior angles of this 12-sided polygon.

Check answer
An -sided polygon can be split into triangles.
Question 5

Find the sum of the interior angles of this 5-sided polygon.

Check answer
An -sided polygon can be split into triangles.
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