Show that the relative error in computing the volume of a sphere, due to an error in measuring the radius, is approximately equal to three times the relative error in the radius.
Let the error in measuring the radius of a sphere be k%.
Let x be the radius of the sphere and Δx be the error in the value of x.
Hence, we have
∴ Δx = 0.01kx
The volume of a sphere of radius x is given by
On differentiating V with respect to x, we get
We know
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 = 0.01kx
⇒ ΔV = (4πx2)(0.01kx)
∴ ΔV = 0.04kπx3
The percentage error is,
⇒ Error = 0.03k × 100%
∴ Error = 3k%
Thus, the error in measuring the volume of the sphere is approximately three times the error in measuring its radius.