Total: 1. Understanding the number within 100 million 1. 1 (pieces), 10, 100, 100, 1 100 million are all units of counting. 2. What is the relationship between every two adjacent counting units? The propulsion rate of every two adjacent counting units is "10". 3. The method of finding the divisor is called "rounding". 4. Whether to "leave" or "enter" depends on whether the highest digit of the omitted mantissa part is less than 5 or more than 5.5. 1, 2, 3, 4, 5, 6 represents the number of objects. ..... are all natural numbers. The object is not represented by 0. 0 is also a natural number. 6. The smallest natural number is 0. Without the largest natural number, the number of natural numbers is infinite. 7. The forward rate between every two adjacent counting units is ten, which is called decimal counting method. 2. The measurement of angle is 1, such as flashlight, car light and sun. Connection: both rays and line segments are parts of a straight line, and line segments are limited parts of a straight line. The difference is that a straight line has no end, its length is infinite, and it extends to both sides. A ray has only one endpoint and its length is infinite, while a line segment has two endpoints and its length is limited. 4. Both straight lines and rays can extend indefinitely. A line segment can measure its length. The figure formed by two straight lines drawn from a point is called an angle. 6. Represented by the symbol "0". Divide the semicircle into 180 equal parts, and the angle of each part is 1 degree, and record it as 1.7. What is the relationship between acute angle, obtuse angle, right angle, right angle and rounded corner? Right angle =90 degrees, obtuse angle greater than right angle less than right angle, right angle = 180 degrees, fillet =360 degrees, acute angle less than 90 degrees.