Q. The number of diagonals of a polygon of 20 sides is
A) 210
B) 190
C) 180
D) 170
Explanation
(d)
Number of diagonals in a polygon of $n$ sides
$= \ ^{n}C_{2} - n$
Here, $n = 20$
$\therefore$ required number of diagonals $= \ ^{20}C_{2} - 20$
$= \frac{20 \times 19}{2 \times 1} - 20 = 170$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.