1) A square, a regular pentagon, and a regular n-gon surround a point.
The number of degrees in each vertex angle of a regular n-gon is: (n - 2) · 180o / n
We know that each vertex angle of a square has 90o.
Each vertex angle of a regular pentagon has (5 - 2) · 180o / 5 = 108o.
There are 360o around each point.
Subtracting the vertex angle of a square and the vertex angle of a regular pentagon,
we are left with: 360o - 90o - 108o = 162o.
Now we use the formula: (n - 2) · 180o / n = 162o to find the value of n.
(n - 2) · 180o = 162o · n
180o · n - 360o = 162o · n
180o · n - 162o · n = 360o
18o · n = 360o
n = 20