The root number 2 is a mathematical constant, also known as the quadratic root number or square root, expressed as √2. It is an irrational number, that is, it cannot be expressed by the ratio of two integers. Its value is approximately equal to 1.4 14 1356.

The root number 2 was first put forward by Pythagoras, an ancient Greek mathematician. They found that when the two right-angled sides of a right-angled triangle are equal in length, the length of the hypotenuse is twice as long as that of any right-angled side.

The root number 2 is widely used in mathematics, appearing in trigonometric functions, algebra, geometry and physics. It is also the solution of many mathematical problems, such as Pythagorean theorem, square root problem and so on.