# The sum of the interior angles of a triangle is 180º; of a quadrilateral is 360º and of a pentagon is 540º. Assuming this pattern continues, what is the sum of the interior angles of a 10-sided polygon?

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It is the expression in finding the number of triangles in a polygon, where n=number of sides. The sum of interior angles of triangle is 180 degrees. Multiply 180 degrees by the number of triangles in a polygon yields the sum of the interior angles of the same polygon.

Decagon has 8 triangles inside it (10 sides - 2). Multiply the number of triangles by 180 degrees, the result is 1,440 degrees.