Two related quantities, one of which changes and the other changes with it. If the ratio (that is, quotient) of the two numbers corresponding to these two quantities is certain, these two quantities are called proportional quantities, and the relationship between them is called proportional relationship. Represented by letters: If the letters X and Y are used to represent two related quantities and K is used to represent their ratio, the (determined) proportional relationship can be expressed as follows: X. If the constant value in the proportion is called K, and the front and rear terms are X and Y respectively, then k=x/y, and K is the ratio of two numbers.

The change law of two related quantities is in direct proportion: expansion at the same time, contraction at the same time, and the ratio remains unchanged.

Examples of positive proportions:

The perimeter and side length of a square.

The circumference and diameter of a circle

Area/width = length

Triangle: 1/2ab=s

It's all about repairing one and changing another.

If the type is aX=Y, a is constant and XY is proportional.

The significance of positive proportion

(1) ratio: two related quantities, one changes and the other changes. If the ratio (that is, quotient) of the two numbers corresponding to these two quantities is certain, these two quantities are called proportional quantities, and the relationship between them is called proportional relationship. ① Represented by letters: If two related quantities are represented by letters X and Y, and their ratio is represented by K,

(2) Positive proportion is related to the changing law of two related quantities: simultaneous expansion and simultaneous contraction, and the proportion remains unchanged. For example, if the speed of a car is constant, is the distance traveled directly proportional to the time spent?

The above manufacturers are certain, so dividend and divisor represent two related quantities, which are in direct proportion. Note: When judging whether two related quantities are directly proportional, we should pay attention to these two related quantities. Although they are also a quantity, they change with the change of another, but the proportion of the two numbers they correspond to is not necessarily, so they cannot be directly proportional. Such as a person's age and weight.

Considering that some BB will not understand, it's simpler! That is, if one thing increases, another thing increases, he decreases, and the other thing decreases, the relationship between these two things is called direct ratio.

[Edit this paragraph] Examples of positive proportions

Perimeter and side length of a square (ratio 4)

Circumference and diameter of a circle (ratio π)

Example of distance:

(1) the speed is constant, and the distance is proportional to the time.

(2) Time is fixed and distance is proportional to speed.