Eli5 : Derivatives. There is a little detail I am missing which no guide I find seems to explain.

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Ok so derivative are an expression of the rate of change of a function. Cool I get that.

– F(x) = 5 : the product of this function is always 5 there is no increase or decrease so there is no change no matter what X is and it makes sense that the derivative would equal 0.

– F(x) = 5x : it is obvious that each time x increases by 1 the product of this function increases by 5. I get it.

– F(x) = x² => F'(x) = 2x : starting from here the numbers stop matching and make me feel like I am missing something. F'(1) = 1. This makes perfect sense. F(x) did in fact increase by 1 when going from F(0) to F(1). Then I try F'(2) = 2×2 = 4. Huh ? But F(x) only increased by 3 between F(1) and F(2) ? Maybe I am looking at the rate of change as compared to F(0) ? after all there is an increase of 4 between F(0) and F(2). Let’s check with 3 then. F'(3) = 6. Wtf ?!

I don’t get it what does it mean when F'(2) = 4 ? When X = 2 then …? and what does it tell me about the original function. Thanks and hope my english isn’t too awfull.

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Anonymous 0 Comments

The derivative function helps us see when the original function is increasing (derivative positive) or decreasing (derivative negative). You can graph this to see.

Rate of change for this is also instanaeous. You averaged the change, that doesn’t tell you how much the function is currently changing.

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