Application of Derivatives


   
 
Approximations by Differentials
Let y = f (x) be a differentiable function of x, errors in x and y are denoted by dx and dy, we have
 
 
 
\ Error in y = f ' (x) dx.
 
Note 1:
 
 
Note 2:
 
 
Note 3:
 
dy and dy are not usually the same and dy is the approximate value of dy.
 
 
Note 4: dx and dy are called the differentials of x and y respectively.
 
Example:
 
Find the approximate value of fourth root of 82 upto 3 decimal places.
 
Solution:
 
Let y = f (x) = x1/4
 
 
Let x = 81, dx =1. Taking these values we have
 
 
 
 
 
     
   
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