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Average and Instantaneous Rate of Change
Dependent and Independent Variables: 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 or
behaves independently, so we call it the independent variable. But the behavior of . So we call it dependent variable.
depends on the 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 value , and changes from an initial value . to the final value , then changes from an initial
to the final value Thus, the increment in Produces a corresponding increment in
Average Rate of Change:
If change of
is real valued continuous function in the interval with respect to over this interval is
, then the average rate of
But
Instantaneous Rate of Change: If rate of change of is real valued continuous function in the interval with respect to over this interval is , then the average
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 velocity is and are given by and , then the average rate of change or the average
Also, the instantaneous rate of change of distance or instantaneous velocity is
Examples of Average and Instantaneous Rate of Change
Example: Let (a) Find the average rate of change of with respect to over the interval (b) Find the instantaneous rate of change of with respect to at the point Solution: (a) For Average Rate of Change: We have . .
Put
Again Put
The average rate of change over the interval
is
(b) For Instantaneous Rate of Change: We have
Put
Now, putting
then
The instantaneous rate of change at the point
is
. Example: A particle moves on a line away from its initial position so that after seconds it is
feet from its initial position. (a) Find the average velocity of the particle over the interval (b) Find the instantaneous velocity at . Solution: (a) For Average Velocity: We have .
Put
Again Put
The average velocity over the interval
is
(b) For Instantaneous Velocity: We have
Put
Now putting
The instantaneous velocity at
is
Example: Use the formula for the area of a circle to find, (a) the average rate of which the area of a circle changes with as the radius increases form . to
(b) the instantaneous rate at which the area of a circle changes with Solution: (a) For Average Velocity: We have Put Again Put The average rate of change from to is
when
(b) For Instantaneous Rate of Change: We have Put
Now putting The instantaneous rate of change at the point is