The sum of angles in a pentagon is 540°. This means that for a regular pentagon, each angle is given as
[tex]\frac{540}{5}=108^{\circ}[/tex]
Observe ΔABC,
ΔABC is an isosceles triangle given lines AB and BC are equal sides of the regular pentagon.
Therefore, summing up the angles in ΔABC,
[tex]\begin{gathered} But
Thus,
Inputting value of
108 + 2(2
