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The number of acute angled triangles whose sides are three consecutive positive integers and whose perimeter is at most 100 is

Question and options

The number of acute angled triangles whose sides are three consecutive positive integers and whose perimeter is at most 100 is
  1. 28
  2. 29
  3. 31
  4. 33

Answer and explanation

Correct answer: B - 29
Sides n-1,n,n+1; acute iff (n+1)^2<(n-1)^2+n^2, i.e. n^2>4n, n>4 (n=4 gives right triangle 3,4,5). Perimeter 3n<=100 gives n<=33. n=5..33: 29 triangles.

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  • IPMAT Indore

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