July 28th, 2013, 06:32 AM  #1 
Senior Member Joined: Oct 2012 Posts: 460 Thanks: 0  chain rule constant rule
Please, How do we get constant rule as a VARIATION OF CHAIN RULE???? Many thanks!!! 
July 30th, 2013, 05:10 PM  #2 
Math Team Joined: Sep 2007 Posts: 2,409 Thanks: 6  Re: chain rule constant rule
Why should we? The "constant rule" (I assume you mean "the derivative of a constant function is 0 for all x") is much more fundamental than the chain rule. I suppose you could argue that, if f(x)= a for all x, then h(x)= f(g(x))= a for all x and any g. By the chain rule, . But clearly, h(x)= f(x) for all x so . That is, we have for all g. Since for all functions, g, is NOT true, we must have . But that seems like using a sledgehammer to kill a fly. 

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