• # question_answer 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

The total number of lines obtained by joining 8 vertices of octagon $={{\,}^{8}}{{C}_{2}}=\frac{8.7}{2}=28$ But out of these 28 lines, 8 are sides and remaining are diagonals. Hence, the number of diagonals $=28-8=20$