Tisch
Teaching objectives:
(1) Master the operation sequence of elementary arithmetic of integers and decimals, use parentheses, and be skilled in calculating elementary arithmetic problems of integers and decimals.
(2) Improve students' abstract generalization ability by summarizing the operation order of elementary arithmetic of integers and decimals.
(3) Cultivate students to develop good study habits and improve their computing ability.
Teaching focus:
Master the operation order of elementary arithmetic of integers and decimals.
Teaching difficulties:
Improve students' calculation accuracy and correct use of approximate equal sign.
Teaching process:
First, review preparation
1. Oral calculation
12+0. 12= 7.2-0.2= 3.5÷0.35=
2.95+0.05= 5-0.6= 2.8÷0. 14=
8÷ 12.5= 1.2+2.8-3.99= 4× 1.72=
3.74+6.26= 4.5×6= 0.25×4÷0.2=
2÷4= 20×0.2= 20.75-9.5=
3.5×8×0. 125=
ask questions
(1) What kinds of operations have we learned?
(2) What do we mean by addition, subtraction, multiplication and division? (Addition, subtraction, multiplication and division are collectively called four operations. )
(3) What is the order of integer elementary arithmetic?
Second, learn new lessons.
1. learning example1:3.7-2.5+4.6 = 3.6 × 6 ÷ 0.9 =
(1) Thinking: What are the operations in the above two questions? What is the operation sequence?
(2) Students should make corrections after trial calculation.
3.7-2.5+4.6
= 1.2+4.6
=5.8
3.6×6+0.9
=2 1.6÷0.9
=24
(3) Summarize the operation sequence
Teacher's explanation: addition and subtraction are called first-level operations, and multiplication and division are called second-level operations.
(2) How many levels of operation are there for the above two questions? What is the operation sequence? (① The problem only contains one-level operation, which is calculated from left to right in turn; (2) The problem only includes two-level operation, and it is also calculated from left to right. )
③ Who can summarize the operation sequence of the above two questions in concise language? (If an expression only contains operations at the same level, it should be calculated from left to right. )
2. Research example 2: 35.6-5×1.73 = 6.75+2.52÷1.2 =
(1) How many levels of operation are involved in the above two questions? Which step to do first, and then which step to do?
(2) Students modify after calculation.
(3) summary.
The above two problems are formulas of two-level operation. What level of operation should I do first?
The conclusion is: if an expression has two levels of operation, the second level of operation should be done first, and then the first level of operation should be done.
(4) Practice: Say the operation sequence first, and then count.
①P37 "Do it"; ②3.6÷ 1.2+0.5×5。
Thinking: ① What if I want to calculate 1.2+0.5 first? (in brackets. )
② What should I do if I want to calculate (1.2+0.5) × 5 first? (in brackets. )
Teacher's introduction: The bracket "()" was first used by the Dutchman Gilat in the17th century. The brackets "[]" first appeared in Julius' works in17th century England.
What are the functions of parentheses and square brackets? (Change the operation order in the formula. )
3. Trial case 3: 3.6 ÷ (1.2+0.5) × 5 = 3.69 ÷ [(1.2+0.5) × 5] =
(1) What is the operation order of the two questions? (In an expression, if there are brackets, count the brackets first, then the brackets. )
(2) Students try to do it.
3.6÷( 1.2+0.5)×5
=3.6÷ 1.7×5
3.6÷[( 1.2+0.5)×5]
=3.6÷[ 1.7×5]
=3.6÷8.5
When there are 3.6÷ 1.7 and 3.6÷8.5 in the calculation, the teacher will explain.
In the process of elementary arithmetic, when the quotient of division has many decimal places or cyclic decimal places appear, two decimal places are generally reserved for calculation.
If you want to keep two decimal places, you only need to divide it to which place. (Generally, you only need to divide by the third decimal place, and use the "rounding method" to keep two decimal places. )
After the students continue to calculate, modify it.
3.6÷( 1.2+0.5)×5
=3.6÷ 1.7×5
≈2. 12×5
= 10.6
3.6÷[( 1.2+0.5)×5]
=3.6÷[ 1.7×5]
=3.6÷8.5
≈0.42
Question: Why should we use the equal sign "≈" in the second step and "=" in the third step? (Because 3.6÷ 1.7 cannot be divided in the second step, the approximate value of its quotient should be 2. 12 in the second step, so "√" should be used in the second step; Step 3: 2. 12 times 5, and the product 10.6 is an accurate result, which should be connected by an equal sign. )
4. Summary
What is the (1) equal sign? When do you use the equal sign? (When the division is infinite or the quotient has a large number of decimal places, two decimal places are reserved by "rounding method". In this step of reserving two decimal places for approximation, write an equal sign or so; When taking exact values, use the equal sign. )
(2) How to change the operation order of the formula? (Parentheses and parentheses are ok. )
(3) What is the operation order of the formula with brackets? (In an expression, if there are brackets, count the brackets first, then the brackets. )
Third, consolidate feedback.
1.P38: Do it.
2.P40: 1①②，2①②.
(1) tells the operation sequence;
(2) calculation and inspection;
(3) Revise and summarize the inspection methods.
Checking calculation method: ① original checking calculation; (2) mutual check calculation; ③ Exchange review calculation.
3. Judge which of the following questions is right and which is wrong, and explain the reasons.
( 1)0.8-0.8×0.7=0( );
(2) 1.6+ 1.4×2=6( );
(3)50-3.9+6. 1=40( );
(4)20÷2.5×4=32( );
(5)9.6+0.4-9.6+0.4=0( );
(6)4.8×2÷4.8×2= 1( )。
4.P40:4. Fill in the blanks first, and then list the comprehensive formula.
5. Homework after class: P40:134,234,3.
extreme
Teaching content:
Example 1 and example 2 on page 39 of the textbook.
Teaching objectives:
1, so that students can understand the meaning of primary operation and secondary operation.
2. Make students master the elementary arithmetic progression without brackets and calculate it correctly.
3. On the basis of students' mastery of integer elementary arithmetic and decimal elementary arithmetic, they can summarize the integer and decimal elementary arithmetic.
4. Cultivate students' serious and rigorous attitude.
Teaching process:
First, review and pave the way
(1) Question: What calculations have we learned? After the students answer, tell them that the four operations of addition, subtraction, multiplication and division are collectively called the four operations. )
(2) Fill in the blanks.
① If there is only () or () in a formula, it should be calculated from left to right.
(2) In an equation, if there are () and (), do () before ().
(3) In an equation, if there are parentheses, first calculate ().
Second, new funding.
1. Show topic: Elementary arithmetic of integers and decimals.
2. Introduce four operations: the four operations we have learned, including addition, subtraction, multiplication and division, are collectively called four operations.
3. Teaching examples 1.
(1) blackboard example 1: 3.7-2.5+4.6 3.6× 6 ÷ 0.9
Then ask questions
① What operations are there in these formulas?
On the basis of students' answers, tell students that addition and subtraction are called first-level operations and multiplication and division are called second-level operations.
② What is the operation order of these two formulas?
③ If "one-level operation" is used instead of "addition and subtraction" and "two-level operation" is used instead of "multiplication and division", how to describe the operation order?
According to the students' answers, change the narrative of reviewing the blanks.
To sum up, how to describe this sentence?
According to the students' answers, change the narrative of filling in the blanks and show the conclusion of the textbook.
(2) Students complete the calculation of example 1.
4. Teaching example 2.
(1) Example 2: 35.6-5× 1.73, 6.75+2.52 ÷ 1.2 on the blackboard, and then ask questions.
① How many levels of operation are included in the formula?
② What is the operation sequence?
According to the students' answers, change the narrative of reviewing the blanks and show the conclusion of the textbook.
(2) Students continue to finish what they have not finished. One student is performing on the blackboard, and the rest are written in books. )
(3) Complete the "Do-Do" exercise below Example 2.
5. Summary: Mixed operation has many steps and is prone to mistakes. To cultivate good habits, we should do "one look, two thoughts, three strokes, four calculations and five checks" when calculating. In the formula without brackets, multiply first and then divide, then add and subtract.
Third, consolidate practice.
Fill in the blanks with 1 and (1). (Show, students answer)
① The four operations of addition, subtraction, multiplication and division are collectively referred to as ().
② Addition and subtraction are called () level operations, and multiplication and division are called () level operations.
(3) In an equation, if it only contains operations at the same level, it should be calculated from (); If there are two levels of operations, the first () level operation should be completed before the first () level operation; If there are two kinds of brackets, count the brackets () first, and then the brackets ().
2. Do it according to page 39 of the textbook.
Fourth, homework.
Exercise 10, questions 1 and 4.
Tisso
Teaching objectives:
(1) Combined with the specific situation, we can understand that the operation order of decimal elementary arithmetic is the same as that of integer elementary arithmetic. If we master the operation order of decimal elementary arithmetic, we can correctly calculate decimal elementary arithmetic.
(2) Understand the application value of decimal elementary arithmetic in real life, and use decimal elementary arithmetic knowledge to solve practical problems in life.
(3) further cultivate students' mathematical transfer and analogy ability, so that students can develop the habit of careful calculation and strengthen their confidence in learning mathematics well.
Teaching focus:
Mastering the operation order of decimal elementary arithmetic can correctly calculate decimal elementary arithmetic.
Teaching difficulties:
Master the operation sequence of decimal elementary arithmetic, so that students can understand the mathematical ideas of transfer and analogy and use mathematical knowledge to solve practical problems in life.
Teaching preparation:
Multimedia courseware, exercise card.
Teaching rules:
The new curriculum standard points out that teachers are organizers, guides and collaborators of learning. According to this concept, I follow the principles of "inspiring", "guiding", "exploring" and "releasing". In teaching, I carefully design preview questions to induce students to think, encourage students to sum up and communicate, let students use what they have learned to transfer and analogy, and promote students to internalize and construct new knowledge.
While choosing teaching methods reasonably, I also pay attention to the cultivation of students' thinking ability and learning ability, and integrate learning methods such as observation, comparison, discussion, communication and independent inquiry, so that students can solve new lessons in the order of elementary arithmetic. In teaching, highlight the characteristics of "five concessions": books let students learn by themselves; Let the students ask questions; The law lets students discover; It is difficult for students to discuss; The evaluation involves students. The above "five concessions" are in line with the concept of new curriculum standards, which truly embodies that students are the main body of learning.
Teaching process:
First, create a situation to reveal the topic (about 10 minutes)
1, talk about it.
2. Show the scene map.
Ask the students to clarify the mathematical information in the question and ask their own questions: How many notebooks and 1 pens are left after buying them with 20 yuan? Let the students calculate independently and tell the solution.
3. Review the operation order of integer elementary arithmetic.
Only the operations of addition, subtraction, multiplication and division should be calculated from left to right; If there are both addition and subtraction and multiplication and division, calculate the multiplication and division first, and then add and subtract. For formulas with brackets, count the ones in brackets first, and then the ones in brackets.
4. reveal the topic.
In real life, the unit price of stationery is not only an integer, but also many decimals. Xiaoming is very lucky today. He caught up with the sale promotion of stationery store's anniversary, and the price changed from integer to decimal.
This leads to today's topic: decimal elementary arithmetic. (blackboard writing topic)
Second, organize activities and explore new knowledge. (about 16 minutes)
1, explore independently and try to practice.
Let the students understand that the unit price of stationery has changed, but the idea of solving problems has not changed, so that students can calculate independently. If step-by-step calculation is adopted, students should be encouraged to list their comprehensive formulas according to the problem-solving ideas.
In teaching, students should be guided to understand the consistency between the operation order of the comprehensive formula and the thinking of solving problems, and the important role of brackets in the comprehensive formula. Students who use the comprehensive formula to solve problems at one time should be praised in time.
2. Discuss and summarize.
Guide students to observe and compare these four formulas. Through group discussion, it is concluded that the operation order of decimal elementary arithmetic is the same as that of integer elementary arithmetic.
Design intention: In the teaching of these two links, I ask students to solve the problem of conditional integer first, and then solve the problem of conditional decimal, and then guide students to observe and compare the listed integer formulas and decimal formulas, so that students can deeply understand that the order of decimal elementary arithmetic is the same as that of integer elementary arithmetic, which breaks through the key and difficult points of this class.
Third, practice to consolidate new knowledge. (about 10 minutes)
In order to let students better grasp the operation order of decimal elementary arithmetic and calculate correctly, I designed four exercises.
The first level, I will calculate.
368+32×5-88 15×( 107-35+ 18)
30× [480÷(24-8)] 530+ 12×25 ÷60
Through practice, students can master new knowledge and cultivate their ability of correct calculation.
The second level, I'll solve it.
Let students experience the extensive application of decimal elementary arithmetic in real life and cultivate their ability to solve simple practical problems by using mathematical knowledge.
Fourth, the whole class summarizes and exchanges evaluation. (about 4 minutes)
Classroom summary is a summary of the knowledge learned in this class, and it is also an evaluation of students' learning situation, and it is also an evaluation of students' emotions and attitudes.