Using differentials, find the approximate value of each of the following up to 3 places of decimal.
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Consider y = ![]()
Let x = 81 and Δx = 1. Then, we get
Δy = ![]()
=![]()
![]()
⇒ 
 = Δy + 3
Now, dy is approximately equal to Δy and is given by:
dy = ![]()

= 0.009
Therefore, the approximate value of 
is 3.009.