# Thermal expansion of Sphere

How would one go about writing an expression of the expansion of the volume of a sphere of a given material? I noticed a few sources give it as

$\Delta V= 3\gamma V\Delta T$
where V is the initial volume; $\gamma$ is the expansivity coefficient and $\Delta T$ is change in temperature of sphere.

Other texts leave out the 3, but with everything else the same.

Any suggestions?

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