Need help with implicit differentiation and Pythagorean theorem?

[watchintv]

I'm trying to understand the second problem on this page: https://tutorial.math.lamar.edu/classes/calci/relatedrates.aspx

Why do we multiply 2x by x'?

Surely there must be a simple reason for this. I'm just not sure.

Thanks!

 

[blamocur]

[imath]2xx^\prime = (x^2)^\prime[/imath]

 

[Pedja]

@watchintv https://en.wikipedia.org/wiki/Chain_rule