Question

The number of diagonals that can be drawn by joining the vertices of an octagon, is

• A. 28
• B. 48
• C. 20
• D. None of these

Answer 1

Answer: (C)

20

Number of verticies of octagon $=8$

So umber of lines that can be drawn using $8$ points ${=}^8{C}_2=\frac{8!}{(8-6)!2!}=28$

Number of diagonals $=$ Total number of lines $-$ total number of sides of octagon$=28-8=20$

So option $C$ is correct.