Notes for Direct and Inverse Proportions

The value of a variable is not constant and keeps on changing. There are many quantities whose value varies as per the circumstances. Some quantities have u relation with oilier quantities such that when one changes the other also changes. Such quantities are inter-redated. This is gilled a variation. Variation is of two types: (i) Direct variation and (ii) Inverse variation.

If two quantities are related in such a way that an increase in one quantity leads a corresponding increase in the other and vice versa, then this is a ease of direct variation. Also, a decrease in one quantity brings a corresponding decrease in the other.

Two quantities x and y are said to be in direct proportion, if

Note: I. In a direct proportion two quantities x and y vary with each other such that remains constant.

II. is always a positive number.

III. or k is called the constant of variation.