Three-dimensional target
I. Knowledge and skills
Can judge whether a number is positive or negative, and can represent the opposite quantity in life with positive or negative numbers.
Two. Process and method
Understand the meaning of rational number with examples in life, and realize the necessity of introducing negative numbers and the universality of rational number application.
Three. Emotional attitudes and values
Cultivate students' awareness and ability of positive thinking and cooperative communication.
Emphasis, Difficulties and Keys in Teaching
1. key: correctly understand the meaning of negative numbers and master the method of judging whether a number is positive or negative.
2. Difficulties: correctly understand the concept of negative numbers.
3. Key: create situations, make full use of familiar things around students, and deepen the understanding of negative meaning.
training/teaching aid
Projector.
teaching process
First, classroom introduction
We know that numbers are produced by people in real life, and their needs are constantly expanding. People are counted, sorted and generated 1, 2, 3, …; In order to express "no object" and "blank", the number "0" is introduced, and sometimes integer results can not be obtained in measurement and distribution, so fractions and decimals are produced.
In our daily life, production and scientific research, we often encounter problems in the representation and operation of numbers, such as the four problems mentioned on pages 2 to 3 of the textbook. The new figures here are -3, -2 and -2.7%. In the previous practical problems, it was expressed as -3 degrees Celsius and the net loss was 2.7%.
Second, teach new lessons.
Numbers such as (1), -3, -2, -2.7% (that is, numbers with minus sign except 0) are called negative numbers, while 3, 2, and +2.7% in the question represent 3 degrees Celsius above zero, with a net victory of 2 goals, an increase of 2.7%, which is contrary to negative numbers. Sometimes positive numbers are preceded by a plus sign. For example, +3, +2, +0.5,+,… means 3, 2, 0.5, … The+and-symbols before a number are called its symbols, which are called attribute symbols.
(2) In ancient China, calculation sheets (tools for representing numbers) were used for calculation, with red calculation sheets representing positive numbers and black calculation sheets representing negative numbers.
(3) The number 0 is neither positive nor negative, but 0 is the dividing line between positive and negative numbers.
(4), 0 can indicate no, also can indicate a certain amount, such as today's temperature is 0℃, indicating a certain temperature; 0 above sea level means the average height of sea level.
Use positive numbers and negative numbers to represent quantities with opposite meanings.
(5) Divide numbers other than 0 into positive numbers and negative numbers, which are derived from quantities representing two opposite meanings. Positive numbers and negative numbers are widely used in many aspects. When expressing the height of a place on a topographic map, it is necessary to take the sea level as the benchmark. Usually positive numbers are used to indicate the height of a place above sea level, and negative numbers are used to indicate the height of a place below sea level. For example, Mount Everest is 8844m above sea level, and Turpan Basin is -65438.
(6) Ask students to explain the meanings of positive numbers and negative numbers in figures 1. 1-2 and 1. 1-3.
(7) Can you give some examples of expressing quantity with positive and negative numbers?
(8). For example, a positive number is usually used to indicate the distance that a car travels eastward, and a negative number is used to indicate the distance that a car travels westward; Use a positive number to indicate the height of water level rising, and use a negative number to indicate the height of water level falling; Use a positive number to indicate the number of things bought, and a negative number to indicate the number of things sold.
Third, consolidate the practice.
The third page of the textbook, exercises 1, 2, 3, 4.
Fourth, class summary.
In order to express quantities with opposite meanings in real life, we introduce negative numbers. Positive numbers are the numbers we have learned in the past (except 0). Adding a "-"sign before a positive number is a negative number, but it cannot be said that "a number with a positive sign is a positive number and a number with a negative sign is a negative number". Adding a negative sign before a number means that the number has the opposite meaning. If the original number is negative, we can't say that. "
Verb (abbreviation for verb) assignment
1. Exercise on page 5 of textbook review 1. 1, consolidate 1, 2, 3.
Sixth, blackboard design
1. 1 positive and negative numbers