Proportion is a mathematical term, meaning that two or more formulas are equal. In a proportion, the product of two external terms is equal to the product of two internal terms, which is called the basic property of proportion.

In mathematics, if the change of one variable is always accompanied by the change of another variable, then these two variables are proportional, and if these changes are always linked by a constant multiplier, then this constant is called a proportional coefficient or a proportional constant.

For example:

(1) The formula for expressing two equal ratios is called ratio, such as 3:4=9: 12, 7:9=2 1:27.

There are four items in the proportion, namely two internal items and two external items; In 7:9=2 1:27, 7 and 27 are called external proportional terms, and 9 and 2 1 are called internal proportional terms.

For example, both teachers and students have met the requirements.

For example, among the goods sold, there are many domestic products.

(4) After the proportion is written as a fraction, then the denominator on the left and the numerator on the right are internal terms; The numerator on the left and the denominator on the right are external terms.

⑤ Basic property of proportion: In a proportion, the product of two external terms is equal to the product of two internal terms.