"Addition of Rational Numbers" PPT courseware

Description

"Addition of Rational Numbers" PPT courseware

Teaching process

Introduction

1. Review questions

1. Among the following sets of numbers, which number has the larger absolute value?

(1) 7 and 4; (2) -7 and 4; (3) 7 and -4; (4) -7 and -4.

2. Explain the actual meaning of the following quantities represented by negative numbers.

(1) Xiaolan moved forward 5 meters for the first time, and then moved forward -2 meters in the same direction;

(2) The temperature in Beijing rose by 3℃ on the first day and -1℃ on the second day;

(3) After Dongfang Car walked 4 kilometers eastward, it then walked eastward -2 kilometers.

3. Based on the above questions, answer

(1) How many meters did Xiaolan advance in total during the two times?

(2) How many degrees did the temperature in Beijing rise in two days?

(3) How many kilometers did Dongfang Car travel eastward?

2. Dynamic demonstration, classification and induction, summary rules

Question 1: On the east-west road, Xiao Ming starts from point O and walks 5 meters for the first time, and continues to walk 3 meters for the second time. Ask Xiao Ming how many meters he walked eastward in the two times?

Situation in the same direction: (1) Walk 5 meters eastward, and then walk 3 meters eastward. How many meters did you walk eastward twice?

(2) Walk east -5 meters, then walk east -3 meters. How many meters did you walk east in total?

Conclusion: To add two numbers with the same sign, take the same sign and add the absolute values.

(3) Walk 5 meters east, and then -3 meters east. How many meters did you walk east in total?

(4) Walk east for -5 meters, and then walk east for 3 meters. How many meters did you walk east in total?

Conclusion: To add two numbers with different signs whose absolute values ​​are not equal, take the sign of the addend with the larger absolute value, and subtract the smaller absolute value from the larger absolute value.

Rational number addition rule

1. To add two numbers with the same sign, take the same sign and add their absolute values.

2. When the absolute values ​​of two numbers with different signs are equal, the sum is 0; if the absolute values ​​are not equal, take the sign of the number with the larger absolute value and subtract the smaller absolute value from the larger absolute value.

3． If you add a number to 0, you still get this number.

Operation steps:

1. First determine the type (same number, different number, etc.);

2. Determine the sign of the sum again;

3. Then perform addition and subtraction of absolute values.

5. Set up problems and strengthen key

Determine right and wrong and correct them

(1) Add two negative numbers and subtract their absolute values;

(2) Add a positive number to a negative number, and the sum is a negative number;

(3) Add a negative number to a positive number, and the sum is a positive number;

(4) When the sum of two rational numbers is negative, both rational numbers are negative.

6. Application examples and consolidation exercises

Example: Calculate the following questions

Exercise 1: Calculate each of the following questions orally and give your reasons

(1)(+4)+(+7); (2)(-4)+(-7); (3)(+4)+(-7); (4)(-4)+(+7 );

(5)(+4)+(-4); (6)(+9)+(-2); (7)(-9)+(+2); (8)(-9)+0

Exercise 2:

1) Calculate:

(1)15+(-22); (2)(-0.9)+1.5; (3)2.7+(-3.5)

2) Use ">" or "<" to fill in the blanks:

(1) If a>0,b>0, then a+b____0;

(2) If a<0,b<0, then a+b____0;

(3) If a>0, b<0,|a|>|b|, then a+b____0;

(4) If a<0,b>0, |a|<|b|, then a+b____0;

7. Course Summary

summary

(1) The main content learned in this lesson;

(2) Key issues in applying the rational number addition rule;

(3) The mathematical thinking methods involved in this lesson.

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Update Time: 2024-07-13

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