JEE Main · 2013 · 07 Apr 2013 · Offline · Permutations and Combinations

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Let be the number of all possible triangles formed by joining vertices of an -sided regular polygon. If , then the value of is
  1. (A)5✓ Correct
  2. (B)10
  3. (C)8
  4. (D)7

Answer: (A)

Solution

The number of triangles from an -gon's vertices is , and the difference . Setting gives , so , i.e. . Taking the positive root, .

JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option

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