Understanding of large numbers

1.1010,000 is 100,000,1010,000 is 1 million,101 million is 10 million,1010 million is 100 million.

The forward rate between two adjacent counting units is "ten", which is called decimal counting method.

Special attention: the difference between counting units and numbers.

2. When using numbers to represent numbers, these counting units should be arranged in a certain order, and their positions are called numbers.

3. Number of digits: A number contains several digits, that is, several digits. For example, 652 100 is a six-digit number.

According to our country's counting habit, every four digits are counted from the right.

6. How to pronounce hundreds of millions or more:

(1) Grading first, starting from high reading. Read level 100 million, then level 10,000, and finally level 1.

(2) Billions should be read according to the pronunciation of billions, and then the word "billion" should be added at the end. Ten thousand series should be read according to the reading method of ten thousand series, and then the word "ten thousand" should be added after it.

No matter how many zeros there are at the end of each level, don't read them. Other numbers have a "0" or several "0" in succession, all of which are read only.

7, hundreds of millions of words:

(1) Write from the top, first write 100 million levels, then write 10,000 levels, and finally write one level.

(2) If there is no unit, just write 0 on the number.

8, compare the size of the quantity:

① For two numbers with different digits, the number with more digits is larger.

(2) Numbers with the same two digits, starting from the most significant digit.

9. Find out the approximate figures:

The mantissa after omitting ten thousand digits depends on the number on one thousand digits; The mantissa after omitting 1 100 million bits depends on the number on1100 million bits.

This method of finding the divisor is called "rounding". Whether it is "rounding" or "decimal" depends on whether the number in the most significant digit of the omitted mantissa is less than 5 or equal to or greater than 5. If less than 5, the mantissa will be discarded; If it is equal to or greater than 5, advance to 1 and then discard the mantissa.

10, indicating the number of objects: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ... are all natural numbers. There is no object, which is represented by 0, and 0 is also a natural number. All natural numbers are integers.

1 1, the smallest natural number is 0, there is no largest natural number, and the number of natural numbers is infinite.

12. The forward speed between every two adjacent counting units is 10. This counting method is called decimal counting method.

13, ON/CE: switch the clear screen key to clear the contents on the display screen.

AC: Clear the key, clear everything.

Second unit

Hectares and square kilometers

The area of a square with a side length of 100 meters is 1 hectare.

1 ha = 1 10,000 m2

2. The square with a side length of 1 km has an area of 1 km2.

1 km2 = 1000000 m2

1 km2 = 100 hectare

3, from large units to small units, multiplied by the rate.

From small units to large units, divided by the forward speed.

4. Square kilometers are suitable for areas with extremely large land area (China, provinces, cities, districts, etc.). ) and marine areas. For example:

The area of the Hong Kong Special Administrative Region is about 1 100 ().

Square, campus and other slightly larger land area is suitable for hectares. For example, Tiananmen Square covers an area of about 44 ();

Playgrounds, classrooms and other small areas are suitable for square meters. For example, the area of a classroom is about 60 ();

5, rectangular area = length x width

Square area = side length × side length

Third unit

Angle measurement

1, line, ray, line segment

Straight line: it can extend to both ends infinitely, and has no end points.

Ray: It can extend infinitely to one end and has only one endpoint.

Line segment: cannot be extended and has two endpoints. A line segment is a part of a straight line.

2. What are the connections and differences between straight lines, rays and line segments?

(1), straight lines and rays can extend indefinitely, so the length cannot be measured.

② The length of the line segment can be measured.

③ A line segment has two endpoints, a straight line has no endpoint, and a ray has only one endpoint.

name

shape

extreme point

expand

line segment

straight

2

cannot

ray

straight

1

One aspect of the matter

straight line

straight

both ends

A figure composed of two rays drawn from a point is called an angle.

4. The measurement unit of angle is "degree", which is represented by the symbol "degree".

Divide the circle into 360 parts, each with an angle of L degrees, and record it as 1.

5. The size of the angle has nothing to do with the length of both sides of the angle. The angle is related to the size of the fork. The bigger the fork, the bigger the angle.

6. The tool for measuring angles is called a protractor.

7. Steps for measuring the angle:

(1) The center of the protractor coincides with the vertex of the angle, and the 0 scale line coincides with one side of the angle.

② The scale on the protractor on the other side of the angle is the degree of this angle.

8. An angle can be regarded as a graph formed by a ray rotating from one position to another around its endpoint.

9. The angle formed by a ray rotating half a circle around its endpoint is called a right angle. 1 boxer = 180

10, a ray rotates around its endpoint to form an angle called a fillet. 1fillet = 360.

1 fillet =2 right angle =4 right angle 1 right angle = 90.

1 1 An angle less than 90 degrees is called an acute angle, and an angle greater than 90 degrees and less than 180 degrees is called an obtuse angle.

acute angle