input: Write a python function to find the largest value from the sum of any two elements in an array.
  assert find_largest_value([1, 2, 3, 4, 5]) == 9
  assert find_largest_value([-1, -2, -3, -4, -5]) == -3
  assert find_largest_value([10, 20, 30, 40, 50]) == 90
output: def find_largest_value(arr):
      arr.sort()
      return arr[-1] + arr[-2]