We can start with the statement that the sum of all exterior angles of a polygon will add 360 degrees.
For example, for the quadrilateral (square):
Then, each exterior angle must have a value of 360/n.
n is the number of sides.
In the case of the square, n is 4.
For a pentagon, n=5.
The interior angles are supplementary of the exterior angles, so they have a value of:
![180-mExt=180-(360)/(n)=180\cdot(1-(2)/(n))](https://img.qammunity.org/2023/formulas/mathematics/college/m2msokv71unkqgulsriu9sop21qw1jbkp0.png)
For a quadrilateral the measure of the interior angle is 90 degrees:
![180(1-(2)/(4))=180(1-(1)/(2))=180\cdot(1)/(2)=90](https://img.qammunity.org/2023/formulas/mathematics/college/at20bpku096i6cjzi8d5hga4w4fj8u9cpn.png)
For a pentagon (n=5), the measure of the interior angle is 108 degrees.
![180(1-(2)/(5))=180\cdot(3)/(5)=108](https://img.qammunity.org/2023/formulas/mathematics/college/k50lmsgtoxd799q1svf18j19tpuq7gt8md.png)
For a dodecagon (n=12), we have a measure of 150 degrees for the interior angle:
![180(1-(2)/(12))=180((10)/(12))=150](https://img.qammunity.org/2023/formulas/mathematics/college/lss48sj182j3r7wge8sseg6eorcx7w75pj.png)