1, calculation rules of fractional multiplication

Fractions are multiplied by integers, and the product of the multiplication of fractions and integers is a numerator, and the denominator remains unchanged; Fractions are multiplied by fractions, the product of numerator multiplication is numerator, and the product of denominator multiplication is denominator. But the numerator denominator cannot be zero.

2, the reciprocal of the score

Find the reciprocal of the fraction, such as 3/4. Switch 3/4 numerator and denominator, so that the original numerator and denominator are the same. It's four-thirds. 3/4 is the reciprocal of 4/3, or 4/3 is the reciprocal of 3/4.

3. Multiply fractions by decimals

Fractions multiplied by decimals can be converted into decimals and then multiplied, or multiplied by decimals. But it is generally used to multiply by decimals because some fractions cannot be converted into finite decimals.

Step 4 multiply the score by the score

Fraction multiplied by fraction: Fraction multiplied by fraction, numerator multiplied by product of numerator, denominator multiplied by product of denominator as denominator.

5. Fractional mixed operation

The order of fractional mixing operation is the same as that of integer mixing operation, that is, if there are parentheses, count the ones in parentheses first, and then count the ones outside parentheses. If there are no brackets, multiply first, then add and subtract. If there is only addition and subtraction, it is calculated from left to right.

6, the reciprocal of an integer

Find the reciprocal of an integer, such as 12, divide 12 into several components, namely 12/ 1, and then exchange the numerator and denominator of the fraction of 12/ 1 with the original numerator as the denominator. Is112,12 is the reciprocal of112.

7, the area of the circle formula:

The size of the plane occupied by a circle is called the area of the circle. πr^2； It is represented by the letter s. The angle of the circle subtended by the arc is half of the central angle. In the same circle or in the same circle, the arcs with equal central angles are equal, the chords are equal, and the distances between chords are equal.

8, perimeter calculation formula

(1) Known diameter: c = π d.

(2) Known radius: c = 2π r

(3) Known perimeter: D=c/π.

(4) Half circumference: 1/2 circumference (curve).

(5) The circumference of a semicircle: 1/2 circumference+diameter (π÷2+ 1).