Then the sum of its internal angles is (N-2)* 180 degrees.

The degree of one of its external angles is between 0 and 180 degrees.

0 & lt600-[(N-2)* 180]& lt； 180

0 & lt960- 180n & lt； 180

960 & gt 180N >780

5.3 & gtN & gt4.3

So N=5.

This polygon is pentagonal.