Algebraic significance: root number 2 is irrational, which is relative to rational number. Rational numbers include integers and fractions. Because it cannot be expressed in the form of integers and fractions, it is called irrational number. Definition: If a positive number A satisfies a 2 = 2, then it is called a= root number 2.

At this point, the number set is extended to the real number set.

Geometric meaning: the diagonal length of a square with a side length of 1 is the root number 2.