Teaching goal: to understand the method of fractional multiplication and division and carry out fractional multiplication and division operation.

Second, the key points and difficulties

1. Important: We will use fractional multiplication and division.

2. Difficulties: the flexible application of fractional multiplication and division.

3. Difficulties and breakthrough methods

The operation of fractions is based on rational numbers and algebraic expressions, and factorization is the means. After transformation, it can often be regarded as the operation of algebraic expressions. The law of multiplication and division of fractions and the order of operation can be obtained by analogy with the relevant contents of fractions. Therefore, teaching students the mathematical thinking method of analogy can better realize the transformation of new knowledge. As long as this is done, students can give full play to their subjectivity and take the initiative to acquire knowledge. Teachers should focus on explaining the related contents of fractions different from fractional operation.

Third, the intention analysis of examples and exercises

1.P 13 In this section, we still use the question 1 to find the volume height. Question 2 is how many times the working efficiency of a large tractor is that of a small tractor. The volume height obtained from these two examples is that the working efficiency of large tractors is twice that of small tractors, which leads to the practical significance of fractional multiplication and division, and further leads to P 14[.

2.P 14 cases 1 is calculated by fractional multiplication and division. Note that if the calculation result can be simplified, it should be simplified to the simplest.

3.P 14 Example 2 is a complicated fractional multiplication and division method. The numerator and denominator of a fraction are polynomials, so polynomials should be factorized first and then simplified.

4.P 14 example 3 is an application problem, with easy-to-understand meaning and easy-to-list formula, but it should be noted that according to the actual meaning of the problem, A >；; 1, so (a- 1) 2 = A2-2A+ 1

Fourth, classroom introduction

1. Show P 13 The problem introduced in this section 1 Find the large volume, and the problem 2 is to find the working efficiency of a large tractor twice that of a small tractor.

[Introduction] From the above problems, it can be seen that the multiplication and division of fractions is sometimes needed. In this section, we will discuss the relationship between multiplication and division of quantity and fraction. Let's start with the multiplication and division of fractions, and compare the multiplication and division rules of fractions.

1.p 14 [Observation] From the above formula, we can see the law of multiplication and division of fractions.

3. [Question] P 14 [Thinking] The multiplication and division method of analogy scores. Can you tell the multiplication and division of fractions?

Similar to the multiplication and division of fractions, the conclusion of multiplication and division of fractions is drawn.

Example explanation of verb (abbreviation of verb)

P 14 case 1.

[Analysis] This example directly applies the fractional multiplication and division method to the operation. It should be noted that the operation result should be simplified, and it should also be noted that in calculation, like algebraic expression operation, the operation symbol is judged first, and then the result is calculated.

P 15 cases 2.

[Analysis] The numerator and denominator of the score in this example are polynomials, so the polynomial should be factorized first and then simplified. If the denominator of the results is not a single polynomial, then it is not necessary to expand them by multiplying them by multiple polynomials.

P 15 case.

[Analysis] There are two problems with this application problem. The first question is: what kind of wheat yield per unit area? Firstly, calculate the areas of "Fengshou 1" and "Fengshou No.2" wheat experimental fields respectively, and then calculate the yield per unit area of "Fengshou 1" and "Fengshou No.2" wheat experimental fields respectively, and take the larger value of the above two scores. According to the actual meaning of the problem, a >: 1, so (a- 1) 2 = A2-2A+ 1

Six, in-class exercises

calculate

( 1) (2) (3)

(4)-8xy (5) (6)

Seven, after-school exercises

calculate

( 1) (2) (3)

(4) (5) (6)

Eight, the answer:

( 1)ab (2) (3) (4)-20x2 (5)

(6)

(1) (2) (3) (4)

(5)(6)& lt； /a2-2+ 1, that is, (a- 1) 2.