# Internal Angles of Regular Polygon

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## Theorem

The size $A$ of each internal angle of a regular $n$-gon is given by:

- $A = \dfrac {\paren {n - 2} 180 \degrees} n$

### Corollary

The internal angles of a square are right angles.

## Proof

From Sum of Internal Angles of Polygon, we have that the sum $S$ of all internal angles of a $n$-gon is:

- $S = \paren {n - 2} 180 \degrees$

From the definition of a regular polygon, all the internal angles of a regular polygon are equal.

Therefore, the size $A$ of each internal angle of a regular polygon with $n$ sides is:

- $A = \dfrac {\paren {n - 2} 180 \degrees} n$

$\blacksquare$

## Also presented as

This formula can also be seen presented as:

- $A = 180 \degrees - \dfrac {360 \degrees} n$