- #1

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- TL;DR Summary
- I am confused by the surface area of a sphere using dA. Not sure why the other side can't just be ##Rd\phi##

Below is an image to calculate the surface area of a sphere using dA. I can see how ##rcos\theta d\phi## works, but I don't understand how that side can't just be ##rd\phi## with a slanted circle representing the arc length. The second part I don't understand is why it is integrated from ##\frac{\pi}{2}## to ##\frac{-\pi}{2}##