A variable which can assign any value independently is called **independent variable **and the variable which depends on some independent variable is called the **dependent variable**.

**For Example: **

** **

If etc, then

We see that as behaves independently, so we call it the independent variable. But the behavior of or depends on the variable . So we call it dependent variable.

__Increment__:

Literally the word increment means on increase, but in mathematics, this word covers both increase as well as decrease; for the increment may be positive or negative. Briefly and simply, the word increment, in mathematics means, “the difference between two values of variables”.

i.e., the final value minus the initial value is called an **increment **in the variable. The increment in is denoted by the symbols or (read as “delta ”)

If , and changes from an initial value to the final value , then changes from an initial value to the final value .

Thus, the increment in ‘’

Produces a corresponding increment in ‘’** **

** **

__Average Rate of Change__**:**

If is real valued continuous function in the interval , then the average rate of change of ‘’ with respect to ‘’ over this interval is

But

__Instantaneous Rate of Change__:

If is real valued continuous function in the interval , then the average rate of change of ‘’ with respect to ‘’ over this interval is

But

This shows that , as

** Average or Instantaneous Rate of Change of Distance**:

**OR**

**:**

__Average or Instantaneous Velocity__Suppose a particle (or an object) is moving in a straight line and its positions (from some fixed point) after times and are given by and , then the **average** **rate of change or the average velocity **is** **

** **

Also, the

**instantaneous rate of change of distance or instantaneous velocity**is