Question 1024085
The answer is (N-2)180 and the induction is as follows -

A triangle has 3 sides and 180 degrees
A square has 4 sides and 360 degrees
A pentagon has 5 sides and 540 degrees

The relation between N sides and degrees, is (N-1)180

Try drawing the 3 figures. Draw one diagonal to cut the square into 2 triangles. Not draw 2 lines in the pentagon from one vertex, to make 3 triangles. Each triangle has 180 degrees.