Two related quantities, one change and the other change; If the ratio of the corresponding two numbers in these two quantities is certain, these two quantities are called proportional quantities, and their relationship is called proportional relationship.

If the letters X and Y are used to represent two related quantities and K is used to represent their ratio (certain), the positive proportional relationship can be expressed by the following formula:

Y:x=k (certain).

Second, the method of judging the positive proportional relationship

1, these two quantities are considered as related quantities.

2. If the ratio (i.e. quotient) of the corresponding two numbers in these two related quantities is certain, the two quantities are in direct proportion, otherwise they are not.

Third, the significance of inverse proportion

Two related quantities, one change and the other change; If the product of the corresponding two numbers in these two quantities is certain, these two quantities are called inverse proportional quantities, and their relationship is called inverse proportional relationship.

If the letters X and Y are used to represent two related quantities and K is used to represent their ratio (certain), the positive proportional relationship can be expressed by the following formula:

Xy=k (certain).

Fourth, the judgment method of inverse proportional relationship

1, these two quantities are considered as related quantities.

2. If the product of the corresponding two numbers in these two related quantities is certain, if the product is certain, these two quantities are inversely proportional, otherwise they are not.