polynomial.rb

def polynomial(numbers, x)
  r = 0
  numbers.each_with_index do |n, i|
    r += n * x**i
  end
  r
end

def polynomial2(numbers, x)
  ary = [1, x]
  (numbers.size - 2).times do |i|
    ary << ary[-1] * x
  end

  r = 0
  numbers.each_with_index do |n, i|
    r += n * ary[i]
  end
  r
end

#   a0 + a1*x + a2*x**2 + a3*x**3 + a4*x**4 ...
# = a0 + x * (a1 + a2*x + a3*x**2 + a4*x**3 ... )
# = a0 + x * (a1 + x * (a2 + a3*x + a4*x**2 ... ) )
def polynomial3(numbers, x)
  # 力尽きた
end