First, multiplication skills:

1, multiplicative commutative law: a * b = b * a

2. Multiplicative associative law: a*b*c=(a*b)*c=a*(b*c).

3. Multiplication distribution law: (a+b) * c = a * c+b * c; (a-b)*c=a*c-b*c .

Two, vertical calculation multiplication should pay attention to four issues:

1, the last digit of two numbers should be aligned.

2. Write as many numbers as possible above, and write as few numbers as possible below to reduce the times of multiplication.

3. If there is a "0" at the end of both numbers, the last digit of the number can only be aligned before the "0" when writing vertically, and finally the number "0" owned by the two numbers after vertical product is added.

4. Decimal multiplication should determine the position of the decimal point of the product according to the multiple of the decimal.

Related information:

Multiplication can also be seen as calculating the objects arranged in a rectangle (integer) or finding the area of a rectangle with a given side length. The area of the rectangle does not depend on which side is measured first, which shows the exchange property. The product of two measured values is a new type of measurement, for example, multiplying the length of two sides of a rectangle to get its area, which is the theme of size analysis.

The common methods of using pencil and paper multiplier need a small number (usually any two numbers between 0 and 9) to store or query the product multiplication table, but a farmer multiplication algorithm does not need it.

Multiplying a number with multiple decimal places is troublesome and error-prone. The universal logarithm was invented to simplify this calculation. The slide rule allows numbers to be quickly multiplied by about three digits of precision. Since the early 20th century, mechanical calculators, such as Marchant, have automatically multiplied as many as 10 digits. Modern electronic computers and calculators greatly reduce the need for manual multiplication.

Multiplication is one of the basic operations in mathematics. Suppose a times b equals c, which is ab? =? C or a.b. = C.

In ancient China, multiplication was carried out by several chips. There are three layers in calculating multiplication: the upper layer is the multiplicand, the middle layer is the product and the lower layer is the multiplier. Multiply the multiplicand by the largest bit of the multiplier, remove the calculation of this bit after multiplication, multiply it by the second bit, and add the numbers on the corresponding bits of the two products until the multiplication is over.