A) 25
B) 20
C) 15
D) 16
Correct Answer: B
Solution :
Each internal angle of polygon \[=\,\,\frac{(n-2)\times 180{}^\circ }{n}\] Each exterior angle of polygon \[=\frac{360{}^\circ }{n}\,\,\,\Rightarrow \,\,\,\frac{(n-2)\times 180{}^\circ }{n}=\frac{3\times 360{}^\circ }{n}\] \[\therefore \,\,\,\,n=8\] \[\therefore \] Number of diagonals of polygon \[=\,\,\,\frac{n(n-3)}{2}=\frac{8\times 5}{2}=\underline{\mathbf{20}}\]
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