1 decimeter = 100 mm
1 m = 10 decimeter =100 cm =1000 mm.
Area: 1 m2 = 100 square decimeter.
1 square decimeter = 100 square centimeter
1 km2 = 100 hectare
1 ha = 1 10,000 m2
Rmb: 1 yuan = 10 jiao.
1 angle = 10 point 1 yuan = 100 point.
Ratio size (compare decimal size)
1, the method of comparing the sizes of two decimals: look at the integer part first, and the decimal with the larger integer part will be larger; If the integer parts are the same, then look at the decimal, and the decimal with a large number on the decimal will be large. ...
2. Put several decimals in order: compare their sizes first. Then put them in order according to the requirements of the topic. When the different quantities of several units are relatively large, the units of these quantities should be unified first, and then compared according to the decimal size comparison method. Finally, the answers should be arranged according to the original numbers given in the most important item.
Addition and subtraction of decimals
1, the meaning of decimal addition and subtraction: the meaning of decimal addition and subtraction is the same as that of integer addition and subtraction. The meaning of decimal addition: the operation of combining two numbers into one number. ② The significance of decimal subtraction: knowing the sum of two addends and one of them, and finding the other addend.
2. Basic properties of decimals: Add "0" or remove "0" at the end of decimals, and the size of decimals remains unchanged.
3. Decimal addition and subtraction calculation rules: decimal point alignment; According to the law of integer addition and subtraction. Count from bottom to top; Which numbers add up to ten and which numbers add up to one. If there are not enough digits at the end of the decimal, you can add "0" and then subtract it. If there are not enough digits in the number, subtract one from the previous digit and add ten to the standard before subtracting. The decimal point of a number must be aligned with the decimal point of a horizontal line.
4. The order of decimal addition and subtraction mixed operation is the same as that of integer addition and subtraction mixed operation. Operation at the same level, from left to right; Parentheses, first inside and then outside.
5. The operation law of integer addition and subtraction is also applicable to decimal addition and subtraction.
Unit 2: Triangle
Understanding of "Space and Graphics"
First, understand graphics.
(1) displays plane graphics and three-dimensional graphics;
② Plane graphics are divided into two categories according to whether they are surrounded by line segments. One is surrounded by a curve and the other is surrounded by a line segment. 20 17 summary of knowledge points in the second volume of fourth-grade mathematics. Beijing normal university edition 20 17 summary of knowledge points in the second volume of fourth grade mathematics. (3) According to the number of edges of the graph.
2. The nature of parallelogram and triangle: triangle is stable, while parallelogram is easily deformed (unstable).
Triangular classification
1. Classify triangles according to different standards and explain the basis of classification.
(1) By angle: right triangle, acute triangle, obtuse triangle.
A triangle with three acute angles is an acute triangle.
A triangle with right angles is a right triangle.
A triangle with an obtuse angle is an obtuse triangle.
(2) Divided by sides: isosceles triangle, equilateral triangle and arbitrary triangle.
A triangle with equal sides is an isosceles triangle.
② A triangle with three equal sides is an equilateral triangle.
2. Through classification, it is found that the equilateral triangle is a special isosceles triangle.
The relationship between the sum of internal angles of a triangle and its sides.
1, and the sum of the internal angles of any triangle is equal to 180 degrees.
2. The sum of any two sides of a triangle is greater than the third side.
3. Some simple problems can be solved by applying the properties of the sum of the angles in the triangle and the relationship between the sides of the triangle.
4. The sum of internal angles of quadrilateral is 360 degrees.
5. Two identical triangles can be used to form a parallelogram.
6. Two identical right triangles can be combined into a parallelogram, a rectangle and a big triangle.
7. Two identical isosceles right triangles can be combined into a parallelogram and a square. Large isosceles right triangle.
Classification of quadrilateral
1, a closed figure surrounded by four line segments is called a quadrilateral. Two sets of quadrangles with parallel opposite sides are parallelograms, and only one set of quadrangles with parallel opposite sides is trapezoid.
2. Rectangular and square are special parallelograms. A square is a special rectangle. 2065438+2007 Four-grade Mathematics Volume II Knowledge Point Summary Beijing Normal University Edition Learning Summary.
3. Square, rectangle, isosceles trapezoid, diamond, isosceles triangle, equilateral triangle and circle are axisymmetric figures.
A square has four axes of symmetry.
② A rectangle has two symmetrical axes. Diamonds have two axes of symmetry.
③ The isosceles trapezoid has 1 symmetry axis.
④ An equilateral triangle has three axes of symmetry.
⑤ A circle has countless symmetry axes.
Unit 3: The Significance of Decimal Multiplication
knowledge frame
1, stationery store (decimal times integer)
2. Decimal point movement (the law of decimal point size change caused by decimal point position movement)
3. Street Park (the relationship between the decimal places of two multipliers and the decimal places of the product)