0 is neither positive nor negative, positive is greater than 0 and negative is less than 0.

Unit 2:

Area of parallelogram = base height S = a h

Area of triangle = base height 2 S = a h 2

Trapezoidal area = (upper bottom+lower bottom) height 2 S = (a+b) h 2

A parallelogram can be divided into two identical triangles; Two identical triangles can form a parallelogram.

A parallelogram can be divided into two identical trapezoids; Two identical trapezoids can form a parallelogram.

The areas of triangles with equal bases and equal heights are equal; The area of a triangle is half that of a parallelogram with equal base and equal height.

Unit 3:

Fractions with denominators of 10, 100 and 1000 can be expressed in decimals, with one decimal place representing a few tenths, two decimal places representing a few percent and three decimal places representing a few thousandths. ...

The first digit to the right of the decimal point is one tenth, and the counting unit is one tenth of 0. 1; The second digit to the right of the decimal point is the percentile, and the counting unit is 0.0 1. The third digit to the right of the decimal point is one thousandth, and the counting unit is 0.005438+0; The propulsion rate between every two adjacent counting units is 10.

It is the nature of decimals to add or remove 0 at the end of decimals, and the size of decimals remains the same. According to the nature of decimals, decimals can usually be simplified by removing the 0 at the end of decimals.

To rewrite a number into a number with "ten thousand" as the unit, just add a decimal point in the lower right corner of the ten thousand digits and then add the word "ten thousand" at the end of the number. To rewrite a number into a number with "100 million" as the unit, just add a decimal point to the lower right corner of this billion bit, and then add the word "100 million" at the end of the number.

Unit 4:

Decimal addition and subtraction calculation method: same digit alignment; From the lowest point: you must enter one at the age of ten or above; If the reduction is not enough, borrow 10 from the previous one and then reduce it.

Unit 6:

Length+width of rectangle = half the circumference of rectangle.

When the perimeter of a rectangle is constant, the greater the difference between length and width, the smaller the area of the rectangle; The smaller the length-width difference, the larger the area of this rectangle.

When the area of a rectangle is constant, the greater the difference between length and width, the longer the perimeter of the rectangle; The smaller the difference between length and width, the shorter the circumference of this rectangle.

Unit 7:

Multiply a decimal by 10, 100, 1000 ... just move the decimal point of this decimal by one, two or three places to the right ...; Move the decimal point to the right by one, two or three places ... This decimal point is enlarged by 10 times, 100 times and 1000 times.

Divide a decimal by 10, 100, 1000. Just move the decimal point of this decimal to the left by one, two or three places ...; Move the decimal point to the left by one, two or three places ... This decimal point is reduced by 10 times, 100 times and 1000 times.

If the dividend is unchanged, if the divisor is expanded (or reduced) several times, the quotient will be reduced (or expanded) by the same multiple:

If the divisor remains the same, the dividend will be expanded (or reduced) several times, and the quotient will be expanded (or reduced) by the same multiple.

Dividend and divisor are expanded (or reduced) by the same multiple at the same time, and the quotient remains unchanged.

Unit 8: 100

1. Length unit:

Millimeter centimeter minute meter kilometer

10 10 10 1000

2. Area unit:

Measure and calculate the land area, usually in hectares. Square land with side length 100 m and area 1 hectare.

Measure and calculate a large area of land, usually in square kilometers. Square land, side length1000m, area

1 km2. 1000000

Square centimeter square decimeter square hectare square kilometer

100 100 10000 100

3. Weight unit: grams (g) kilograms (kg) tons (t)

1000 1000

4. unit of volume: milliliter (ml) liter (l)

1000

Unit 9:

Calculation algorithm of decimal multiplication;

1. Calculate by integer multiplication;

2. Observe the decimal places in the factor * * *(factor * * *) and count the same decimal places from the right side of the product.

Calculation method of fractional division:

1. Convert the divisor into an integer according to the principle of quotient invariance;

2. Calculation method according to integer division;

3. The decimal point of quotient should be aligned with the decimal point of dividend;

4. If there is a remainder, you can continue to divide it according to the nature of the decimal.

Multiply a nonzero number by a number less than 1, and this number will be smaller than the original one. For example: 25.6 0.3 5.6

A decimal number or multiple numbers appear repeatedly from a certain position in the decimal part. Such decimals are called cyclic decimals. One or more numbers that appear repeatedly in turn are the cyclic part of this cyclic decimal.