Important knowledge points of mathematics in grade four
Parallelogram and trapezoid
1, understanding parallelogram and trapezoid
① quadrilateral classification: one is that two groups of opposite sides are parallel respectively; The other is that only one group of opposite sides are parallel.
② Parallelogram: Two groups of parallelograms with parallel opposite sides are called parallelograms. Rectangular and square are special parallelograms. A square is a special rectangle.
③ Trapezoid: Only a set of quadrangles with parallel opposite sides is called trapezoid. Trapezoid in life: the cross section of a ladder, dam, etc.
④ Similarities and differences between parallelogram and trapezoid:
Similarities: they are all quadrangles; There are parallel opposite sides.
Difference: two groups of opposite sides of parallelogram are parallel and equal; A trapezoid has only one set of parallel opposite sides, and the two sets of parallel opposite sides are not equal.
2. Characteristics of parallelogram: parallelogram is easy to deform and unstable.
The application of parallelogram instability in life: electric sliding doors on campus, sliding doors on the floor of shops, etc.
3. Names and high drawing methods of parallelogram and trapezoid parts.
① Name the sides of parallelogram and trapezoid.
Base and height of parallelogram: Draw a vertical line from a point on one side of parallelogram to the opposite side. The line segment between this point and the vertical foot is called the height of the parallelogram, and the side where the vertical foot is located is called the bottom of the parallelogram.
② A group of parallel opposite sides in a trapezoid, the shorter side is called the upper bottom of the trapezoid, the longer side is called the lower bottom of the trapezoid, and the non-parallel group of opposite sides is called the waist of the trapezoid.
③ isosceles trapezoid: isosceles trapezoid.
④ Right-angled trapezoid: When a waist is perpendicular to the upper and lower soles, this trapezoid is called right-angled trapezoid.
⑤ Attention should be paid when drawing the height: the height to be drawn should be indicated by a dotted line; Be sure to draw off the foot symbol.
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.
Articles related to important basic knowledge points of mathematics in grade four;
★ Basic knowledge points of mathematics in the first volume of the fourth grade
★ Basic knowledge points of mathematics in the fourth grade of primary school
★ Basic knowledge points of the fourth grade mathematics text
★ Basic knowledge points of mathematics in the fourth grade of primary school
★ Summary of basic knowledge points of mathematics in grade four
★ Review the basic knowledge points of fourth grade mathematics.
★ Basic knowledge points of fourth grade mathematics
★ Important knowledge points of fourth grade mathematics
★ Important knowledge points of mathematics in the fourth grade of primary school
★ People's Education Edition fourth-grade mathematics knowledge points combing