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
Irrational number the coefficients formula_7 are integers and formula_8. Any rational root of this polynomial equation must be of the form "r" /"s", where "r" is a divisor of "a" and "s" is a divisor of "a". If a real root formula_9 of a polynomial formula_10 is not among these finitely many possibilities, it must be an irrational algebraic number. An exemplary proof for the existence of such algebraic irrationals is by showing that "x" = (2 + 1) is an irrational root of a polynomial with integer coefficients: it satisfies ("x" − 1) = 2 and hence "x" − 2"x" −