The root number 5 is approximately equal to 2.236. The first method is to use a calculator, and the root number 5 is an infinite acyclic decimal. The second method is to calculate with a pen. First, make sure that the unit number of the root number 5 is 2, and then calculate the values of decimals, percentiles and thousandths in turn by flat method. The radical sign was invented by German mathematician Michael Steefel (1487- 1567). He first used these symbols in 1544.

The root sign is a mathematical symbol. The root sign is a symbol used to represent the root operation of a number or an algebra. If a=b, then a is the n-th root of b or a is the 1/n power of b, and the n-th handwritten and printed characters are represented by, and the number of roots or algebraic expressions are written in the area surrounded by the left side of the symbol and the right side of the horizontal part above the symbol, which cannot be out of bounds.

The root sign is the mathematical expression of the root. The symbol placed in front of the expression indicates that the square root (such as a, a+b, 2) will be used in the expression. If an indicator is added before this symbol, it means to take another corresponding root (if indicator 3 is added, it means that the value range of cube root is greater than or equal to 0). In the range of real numbers: it cannot be negative under even root sign, and its operation result is not negative; It can be negative under the odd root sign. It is not limited to real numbers, that is, when considering imaginary numbers, even the roots can be negative.

Generally speaking, the root number refers to the quadratic root number, that is, the square root of the number below the root number. The number below the root sign is called the "root sign". So the condition that the number under the root sign needs to meet: it is the square of a certain number, that is, it needs to be greater than or equal to 0, that is, it is non-negative. In practical mathematical problems, there are also three numbers and four numbers. That is, the number under the root sign is the root, the fourth power, or the higher power.

Conditions to be met in the real number range: odd root number: that is, odd power of the root number, which can be positive, zero or negative. Even root number: that is, the root number is even and the root number is the same as the root number, that is, it must be non-negative.

The method of finding square root by pen calculation

1. Every two bits from the cell to the left are a segment. If there is a decimal, every two digits from the right of the decimal point are used to separate the parts.

2. Find the complete square number not greater than the first number on the left, which is the "quotient";

3. Subtract the quotient from the first part on the left and write their difference in the second part on the right as the first remainder;

4. Multiply the quotient by 20 and try to divide it by the first remainder to get the largest integer as the trial quotient (if this largest integer is greater than or equal to 10, use 9 or 8 as the trial quotient);

5. multiply the quotient by 20, add the quotient, and then multiply the quotient. If the product obtained is less than or equal to the remainder, write this trial quotient after the quotient as a new quotient; If the obtained product is greater than the remainder, try again by reducing the trial quotient until the product is less than or equal to the remainder;

6. In the same way, keep asking.