Real numbers: Rational numbers and irrational numbers are collectively called real numbers.

Number axis: a directed straight line, and each point represents a real number.

Inverse number: Two numbers with equal absolute values and opposite signs.

Absolute value: the distance between the point of a number and its zero point on the number axis.

Reciprocal: Mathematically, if the product of a number x multiplied by it is 1, then these two numbers are called reciprocal.

Arithmetic square root: Generally speaking, if the square of a nonnegative X is equal to Y, then this nonnegative X is called the arithmetic square root of Y..