[Sum of interior and exterior angles of a polygon] [Sum of angles in a triangle. Theorem of the exterior angle.]

Find the sum of the interior angles:

a) of a quadrilateral;

b) of a convex pentagon

c) of a convex $n$-gon

#
All $n-3$ diagonals of a convex $n$-gon, drawn from an arbitrary vertex, divide it into $n-2$ triangles.

## Otvet

a) $360^{\circ}$;
b) $540^{\circ}$;
c) $180^{\circ}(n-2)$.