1, the fraction is multiplied by the integer, and the product of the numerator of the fraction multiplied by the integer is the numerator, and the denominator remains unchanged.

2. Fractions are multiplied by fractions, the product of numerator multiplication is numerator, and the product of denominator multiplication is denominator.

3. Find the fraction of a number and calculate it by multiplication (a number? = specific quantity). Divide what can be divided before multiplying.

Second, fractional division.

Two numbers whose product is 1 are reciprocal.

2. Dividing a fraction by an integer (except 0) is equal to multiplying this fraction by the reciprocal of this number.

An integer divided by a fraction is the reciprocal of an integer multiplied by this number.

4. The number A divided by the number B (except 0) is equal to the reciprocal of the number A multiplied by the number B..

5. Unit? 1? (a number)? = Specific quantity. How many? Unit? 1? (a number) = a fraction of a known number? How do you find this digital unit? 1? (a number) = specific quantity?

Third, the circle

1, when drawing a circle, the fixed point is the center of the circle, which is generally represented by the letter o.

2. The line segment from any point on the circle to the center of the circle is the radius, which is generally represented by the letter R. The line segment whose two ends pass through the center of the circle is the diameter, which is generally represented by the letter D, and R = D = 2 R.

3. The size of a circle is related to its radius, and its position is related to its center.

The circumference of a circle is always more than three times the diameter. The quotient of the circumference divided by the diameter of a circle is a fixed number. It's called pi, in letters? (read p? I) means. Usually take its approximate value when calculating? =3. 14。

5. perimeter C=? d=2？ r d= =C r= =C？ 2? =C？ 2= C？ 2?

6. circular area S=? r2 =？ ()2

7. Sector area = large circle area-small circle area =? R2 is big? R2 is small =? (r2 is big -r is small 2)

8. The figure enclosed by the two radii of the central angle and the arc of the central angle is called a sector. In the same circle, the size of the sector is related to the central angle of the sector.

Four. Ratio and proportional distribution

1 and the division of two numbers is also called the ratio of these two numbers.

2. The relationship between ratio, division and fraction

The difference between ratio, division and fraction:

What is the ratio of the former to the latter? Species division relationship.

Dividend by division? The divisor quotient is an operation.

Fractional numerator-(fractional line) Denominator Fractional value is a number.

3. The last term of the ratio cannot be 0, just like the divisor and denominator.

This ratio can be expressed in fractions, decimals or integers.

5. The first term and the last term of the ratio are multiplied or divided by the same number (except 0) at the same time, and the ratio remains unchanged, which is called the basic property of the ratio.

6. Distribute the quantity according to a certain proportion. This distribution method is usually called proportional distribution.