A polygon has n sides (n≥3). One vertex is chosen, and all possible diagonals from that vertex are drawn, dividing the polygon into triangles.
a. (i) How many triangles are formed? Express your answer in terms of n and justify it.
b. (ii) Using the result of part (i) and the angle-sum property of a triangle, derive a general formula for the sum of the interior angles of the n-sided polygon.
c. (iii) Apply your formula to find the sum of the interior angles of a regular decagon.