1, axisymmetric transformation: obtained from a plane figure, and the axisymmetric figure is called axisymmetric transformation. Either of the two axisymmetric figures can be regarded as the result of the axisymmetric transformation of the other figure, and an axisymmetric figure can be regarded as the expansion of the axisymmetric transformation based on a part of it.
2. The essence of axisymmetrical transformation: a plane figure can be used to get a figure symmetrical about the straight line I, and the shape and size of this figure are exactly the same as the original figure, and each point on the new figure is a symmetrical point of a point on the original figure about the straight line; The line connecting any pair of corresponding line segments is vertically bisected by the symmetry axis.
3. Absolute value is the distance from a point corresponding to a number on the exponential axis to the origin, which is represented by "||". |b-a| or |a-b| represents the distance between the point representing a and the point representing b on the number axis. In mathematics, the absolute value or the modulus |x| is non-negative, regardless of its sign, that is |x|=x means positive x, |x|=-x means negative x (in this case -x is positive), and |0|=0.
4. Rational number is the collective name of integer (positive integer, 0, negative integer) and fraction, and it is the set of integer and fraction. Integers can also be regarded as fractions with a denominator of one. Real numbers that are not rational numbers are called irrational numbers, that is, the fractional part of irrational numbers is infinite cyclic numbers. It is one of the important contents in the field of number and algebra.