Irrational number number to ratios of continuous magnitude. In his commentary on Book 10 of the "Elements", the Persian mathematician Al-Mahani (d. 874/884) examined and classified quadratic irrationals and cubic irrationals. He provided definitions for rational and irrational magnitudes, which he treated as irrational numbers. He dealt with them freely but explains them in geometric terms as follows: In contrast to Euclid's concept of magnitudes as lines, Al-Mahani considered integers and fractions as rational magnitudes, and square roots and cube roots as irrational magnitudes. He also introduced an arithmetical approach to the concept of irrationality, as he attributes the following to irrational
The Story of the Youth Who Went Forth to Learn What Fear Was attempts to learn fear, which eventually leads to his awareness of mortality. This tale type did not appear in any early literary collection but is heavily influenced by the medieval adventure of Sir Lancelot du Lac called "", where he spends a night in a haunted castle and undergoes almost the same ordeals as the youth. A father had two sons. The younger, when asked by his father what he would like to learn to support himself, said he would like to learn to shudder. A sexton told the father that he could teach the boy. After teaching him to