Length 1, length unit: refers to the basic unit for measuring spatial distance, and is the basic unit formulated by human beings to standardize length. Its international unit is "meter" (symbol "m"), and commonly used units are millimeter (mm), centimeter (cm), decimeter (dm), kilometer (km) and so on. Length units play an important role in various fields.
2. meter: in the international system of units, the standard unit of length is "meter", which is represented by the symbol "m".
3. decimeter: dm is one of the metric units of length, and 1 decimeter is equivalent to one tenth of 1 meter.
4. centimeter: centimeter, length unit. The abbreviation (symbol) is cm. Unit conversion of centimeters:1cm =10 mm = 0.1decimeter =0.0 1 m =0.0000 1 km.
5. Millimeter: English abbreviation mm, forward speed: 1mm = 0. 1cm.
6. Carry: In addition, when each digit is equal to the radix, move forward by one digit.
Angle 1, the dynamic definition of angle: the graph formed by the rotation of light from one position to another around its endpoint is called angle. The endpoint of the rotated ray is called the vertex of the angle, the ray at the starting position is called the starting edge of the angle, and the ray at the ending position is called the ending edge of the angle. ?
2. Type of angle: the size of the angle has nothing to do with the length of the side; The size of an angle depends on the degree to which both sides of the angle are open. The bigger the opening, the bigger the angle. Conversely, the smaller the opening, the smaller the angle. In dynamic definition, it depends on the direction and angle of rotation.
Angles can be divided into acute angles, right angles, obtuse angles, right angles and rounded corners. An angle measuring system in degrees, minutes and seconds is called an angle system. In addition, there are secret system, arc system and so on. ?
Acute angle: An angle greater than 0 and less than 90 is called an acute angle.
Right angle: An angle equal to 90 is called a right angle.
Oblique angle: an angle greater than 90 and less than180 is called obtuse angle.
Multiply 1 in the table to find the sum of several identical addends. Besides addition, multiplication can also be used for simpler expression. ? Multiplication is a simple algorithm to calculate the sum of several identical addends. ?
2. Find the sum of several identical addends and rewrite it into a multiplication formula.
The above are the important knowledge points of mathematics that I have compiled. I hope I can help you.