Ruby Koan 151 raising exceptions

Question

I\'m going through the ruby koans, I\'m on 151 and I just hit a brick wall.

Here is the koan:

# You need to write the triangle method in the file \'trian         


        

Answer 1

def triangle(a, b, c)
  [a, b, c].permutation do |sides|
    raise TriangleError unless sides[0] + sides[1] > sides[2]
  end
  case [a,b,c].uniq.size
    when 3; :scalene
    when 2; :isosceles
    when 1; :equilateral
  end
end