Explanation
The sum of the interior angle of a polygon with \(\mathrm{n}\) sides \(=(n-2) 180^{\circ}\).
Since a pentagon has 5 sides, sum of the interior angles \(=(5-2) 180^{\circ}=540^{\circ}\).
Since the pentagon is regular, the interior angles are equal.
Then, each interior angle \(=\frac{540^{\circ}}{5}=108^{\circ}\)xterior angle \(+\) interior angle \(=180^{\circ}\)xterior angle \(=180^{\circ}-\) Interior angle
Method 2
\(=180^{\circ}-108^{\circ}=72^{\circ}\)
\(\begin{aligned} 1 \text { ext. (regular) } &=\frac{360^{\circ}}{n} \\ &=\frac{360^{\circ}}{5}=72^{\circ} \end{aligned}\)