5. As shown in the figure, there is an isosceles triangle in an equilateral triangle, and

1) There is an isosceles triangle in an equilateral triangle
∠1=∠2=30,∠3=∠4=30
∠5=180-(∠2+∠3)=180-(30+30)=120
2) Sum of internal angles of triangle = (3-2) * 180
Sum of internal angles of quadrilateral = (4-2) * 180
Sum of inner angles of Pentagon = (5-2) * 180
Sum of inner angles of hexagon = (6-2) * 180
find
Sum of inner angles of n-polygon = (n-2) * 180

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