Pretty much the title, Cannot fathom why titled formula is invalid or not in use?
We take half the vertical cirucmference, pi * r and rotate it around the horizontal periphery on its axis, 2 * pi * r, this should give the value of surface area.
Pic just for reference –
https://qphs.fs.quoracdn.net/main-qimg-902ca0ec6c07471c700357a711f7e70c-c
In: Mathematics
Because you can’t just multiply those two values as if the sphere was a square with those side lengths. The shape isn’t flat so when you rotate it around you don’t multiply the values, you need to do integration to find the volume of the solid of revolution. If you do this for the limits of a sphere then you get the formula 4*πr^*2.
Take a look here for a more in depth explanation of the maths. [https://brilliant.org/wiki/surface-area-sphere/](https://brilliant.org/wiki/surface-area-sphere/)
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