First, the angle and right angle of meters and centimeters
1, commonly used length units: meters and centimeters.
2. The measurement unit of shorter objects is usually centimeters, and the measurement unit of longer objects is usually meters.
3. When measuring: aim the "0" scale of the ruler at the left end of the object, and then look at the right end of the note, which is several centimeters.
4. 1m = 100cm 100cm = 1m。
5. Characteristics of line segment: ① The line segment is straight. ② A line segment has two endpoints. ③ Line segments can measure the length.
6. A corner has a vertex and two sides. It is surrounded by rays, not line segments. A ray has only one endpoint, and its length cannot be measured. For example:
(edge)
(vertex)
(edge)
7. Angle drawing: Starting from one point, draw two sides in different directions with a ruler to draw an angle.
You can draw right angles with triangles (textbook 4 1 page legend).
8. Of the three angles on a triangle, 1 is a right angle. Both a square and a rectangle have four corners, which are right angles.
9. To know whether an angle is a right angle, you can compare it with the right angle on a triangle.
10, the size of the angle has nothing to do with the length of both sides, but only with the width of both sides.
An angle greater than or greater than a right angle is less than or less than a right angle.
Second, the pen addition and subtraction within 100
1. When calculating the vertical addition of two numbers: ① The same number is aligned, and a plus sign is written before the last digit is written down.
(2) From the unit.
(3) If one digit exceeds 10, enter 1 into ten digits.
When calculating the subtraction of two digits vertically: ① Align the same digits, and write a negative sign before the descending order of the high digits.
(2) From the unit.
(3) If the number of digits is not reduced enough, 1 is deducted from the number of digits, and the number of digits is reduced to 10 again. Remember to subtract 1 when calculating the number of digits.
2. Estimation: Calculate a number close to a whole hundred as a whole hundred.
Methods: Look less when the unit is less than 5, look more when the unit is equal to or greater than 5, and regard it as the nearest integer ten or integer hundred.
Such as: 49+42≈90 28+45+24≈ 100.
50 40 30 50 20
Note: When the word "about" appears in the question, it needs to be estimated.
3. How much is "one known number" more than "another known number"? Calculate by subtraction, and subtract the smaller number from the larger number on both sides of the word "Bi".
4. More or less known problems. Less than who, with whom to reduce a few; If there are more unknowns than anyone else, add a few more.
Third, table multiplication.
1, the addition of several identical numbers can be expressed by multiplication or addition. It is simpler to express it by multiplication.
2. When adding the same addend to write multiplication, use the same addend × the number of the same addend or the number of the same addend × the same addend.
For example, 5+5+5+5 is 5 × 4 or 4 × 5.
When addition is written as multiplication, the sum of addition is equal to the product of multiplication.
4. In the multiplication formula, two factors exchange positions and the product remains unchanged.
5. Names and calculation formulas of each part of the formula.
Multiplication: factor × factor = product addition: addend+addend = and subtraction: minuend-subtrahend = difference.
Product Factor = Sum of Factors-Addendum = Addendum Minus = Difference+Subtraction
Subtraction = minuend-difference
6. In the multiplication formula of 9, 9 times 9 or 9 times several can be regarded as ten MINUS several, where "several" refers to the same number.
Such as:1× 9 =10-1.9× 5 = 50-5.
7. Look at the picture and write the multiplication, addition and subtraction formulas:
Multiplication and addition: the same part is represented by multiplication first, and then the different parts are added.
Multiplication and division: first calculate each copy as the same, write multiplication, and then subtract the extra part.
When calculating, multiply first, then add, and then subtract.
For example:
Plus: 3+3+3+2 = 14 times: 3×4+2= 14 times minus: 3×5- 1= 14.
8. "How many times is a number?" Calculate by multiplication, and multiply this number by multiples or multiples by this number.
9. There are several identical addends, which are several times of the same addend. Three fives is three times as much as five.
Fourth, the object of observation
1, the left, right or up and down of each graph are the same, so we call such an object symmetrical.
2. Divide the figure into two completely symmetrical parts with a dotted line, which is called the symmetry axis.
3. The reflection is symmetrical up and down. When looking in the mirror, the front and back, up and down positions remain the same, only the left and right positions are reversed.
4. Rectangular, square and circle are symmetrical figures.
A rectangle has two axes of symmetry. A square has four axes of symmetry. A circle has countless axes of symmetry.
Verb (abbreviation for verb) statistics
1, and the word "positive" means the number 5.
2. In the statistical chart, if one cell represents quantity 2, half a cell represents quantity 1.
Sixth, mathematics wide angle
1, when arranging combinations, according to a certain order, so as to avoid duplication or omission.