The radius of a sphere shrinks from 10 to 9.8 cm. Find approximately the decrease in its volume.

Given the radius of a sphere changes from 10 cm to 9.8 cm.


Let x be the radius of the sphere and Δx be the change in the value of x.


Hence, we have x = 10 and x + Δx = 9.8


10 + Δx = 9.8


Δx = 9.8 – 10


Δx = –0.2


The volume of a sphere of radius x is given by



On differentiating V with respect to x, we get




We know




When x = 10, we have.




Recall that if y = f(x) and Δx is a small increment in x, then the corresponding increment in y, Δy = f(x + Δx) – f(x), is approximately given as



Here, and Δx = –0.2


ΔV = (400π)(–0.2)


ΔV = –80π


Thus, the approximate decrease in the volume of the sphere is 80π cm3.


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