The number of diagonals in a septagon is
21
42
7
14
Beginner-friendly steps:
Use the formula for the number of diagonals of an n-sided polygon:
\[ \\text{Diagonals} \\;=\\; \dfrac{n(n-3)}{2} \]A septagon has 7 sides. So put n = 7:
\[ n \\;=\\; 7 \]Find n − 3:
\[ n-3 \\;=\\; 7-3 \\;=\\; 4 \]Multiply n and (n − 3):
\[ n(n-3) \\;=\\; 7 \times 4 \\;=\\; 28 \]Divide by 2:
\[ \dfrac{28}{2} \\;=\\; 14 \]Answer: 14 (Option D).