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No calculus (Posted on 2002-07-31) Difficulty: 4 of 5
Define:
d/dx(f(x)) = f'(x)

where f'(x) = gradient (or slope) of f(x) at x = x.

Prove that:
d/dx(x^2) = 2x

without using calculus.

See The Solution Submitted by Cheradenine    
Rating: 3.2000 (10 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re(3): Hmmmm | Comment 18 of 26 |
(In reply to re(2): Hmmmm by Cheradenine)

"In the version you suggest youre basically removing half of the
problem, plus, in my opinion, making it much less appealing and
interesting to solve. "

While the appeal of "calculus without calculus" is what made you think of the problem in the first place, it is not intrinsic to the problem itself. It works not because you found the derivative of x², but because you exploited a property of the graph of that specific function.

You could express the wonder of "calculus without calculus" in a note at the question, but by phrasing it as a calculus problem and then saying "but don't use calculus" you are only making the problem unecessarily obtuse.
  Posted by TomM on 2002-08-01 08:22:01

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