Knowledge points of "three numbers multiplied by two numbers" in the first volume of mathematics in grade four
1, the method of multiplying three digits by two digits:
Multiply each bit of one factor by each bit of another factor in turn, and then multiply each bit of another factor by ten bits of this factor in turn. When you multiply to which bit, the single bit of the product will be aligned with which bit. When a bit exceeds ten, it will advance to "1" and then add the products of the two multiplications. When there is a zero at the end, align the numbers in front of the two factors 0, multiply them, and then add a few zeros that did not participate in the operation after the product. When there is a 0 in the middle, this 0 will participate in the operation.
2. Variation law of factor and product: If one factor remains unchanged, another factor will be expanded (or reduced) several times, and the product will also be expanded (or reduced) by the same multiple.
3. Estimation method of multiplication of two or three digits: first omit the mantissa behind the digits of two factors, find the divisor, and then multiply the two divisors.
Supplementary knowledge points
1, estimation method: use rounding method to estimate. Is this estimate big or small? That is, the method of estimation;
2. Calculate three digits multiplied by two digits vertically. Note that the end of the product in the second step is written in ten digits.
3. Multiply three digits with zero in the middle or at the end of the factor by two digits.
Multiply the middle by a factor of 0; If there is a zero at the end, align the last digit of the number in front of the two factors, multiply it by the number in front of zero, and then it will return to zero, and several zeros will return to several zeros.
Estimation in real life:
Practical problems in life (is it estimated to be big or small? )
A: 350 students are going out to visit. There are 7 carriages with 56 seats each. How many cars do you need?
B, the bridge weighs 3 tons, the goods are 6 boxes, each box weighs 285 kilograms, and the car weighs 986 kilograms. Can this car cross the road?
Learning point
Methods and precautions of estimation: the coefficient should be estimated as integer ten, integer hundred or integer thousand. When estimating, pay attention to seeking truth from facts and approach the accurate value.
Knowledge points of "angle measurement" in the first volume of fourth grade mathematics
1. Line, light, angle
Straight line: a line that extends infinitely to both ends and has no end.
Ray: it can be like a line extending in one direction, and the ray has an endpoint.
Line segment: a line that cannot be extended. A line segment has two endpoints.
Angle:
A figure composed of two rays with a common endpoint is called an angle.
This common endpoint is called the vertex of the angle, and these two rays are called the two sides of the angle.
2. The connection and difference between straight lines, rays and line segments.
1) Both 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.
3. The characteristics of angle
Mathematics learning methods and skills
1, not only to listen to lectures, but also to think.
Many students can listen carefully in class and have a deep memory of basic knowledge such as formulas and concepts, but they can't do it when they encounter practical problems. Therefore, students should not only listen carefully in class, follow the teacher's ideas, but also think and understand the problem-solving ideas.
For mathematics learning, the most important thing is the cultivation of problem-solving ability and knowledge application ability. If a student only remembers the basic knowledge such as formulas and concepts, but doesn't know how to use these knowledge to solve problems, then his mathematics learning ability is very poor, and his learning efficiency and quality are also very low.
2. Broaden the thinking of solving problems
In mathematics teaching, teachers will guide students to think and find different methods to solve problems. Therefore, students should make good use of these opportunities, broaden their way of thinking and cultivate their own thinking ability. Through these methods, students can exercise their thinking ability and adaptability, learn to draw inferences from others, and thus improve their math scores.
3. Make good use of the wrong set of questions
In the process of learning, students will inevitably make mistakes. At this time, it is necessary to integrate and summarize the wrong questions and establish a set of wrong questions. With the help of the wrong problem set, students can know the reasons for their mistakes, master the correct problem-solving methods and avoid making the same mistakes again. In addition, in the process of learning, we should always look through the wrong set of questions to deepen our impression, so as to remove the shortcomings of knowledge and make up for the loopholes in knowledge.
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