Answer:
Step-by-step explanation:
Consider this regular pentagon .
Let us join vertices and as shown to form three triangles as shown. I have used letters to represent internal angles of triangles for sake of simplicity.
Since the sum of interior angles of a triangle is ,
In △
In △
in △
um of interior angles of the pentagon is
[using the above three results]
∠A + ∠B + ∠C + ∠D + ∠E =
Since it is a regular octagon, ∠A = ∠B = ∠C = ∠D = ∠E
⇒ ∠A + ∠A + ∠A + ∠A + ∠A =
⇒ \
Hence internal angle of a regular pentagon is