Use the definition of the derivative to find f'(x)
if f(x) = 2x / (x=4)

Does this mean first principles?

Question

Use the definition of the derivative to find f'(x)
if f(x) = 2x / (x=4)

Does this mean first principles?

myininaya · Answer

So you are finding the derivative of f(x)=2x at x=4?

myininaya · Answer

$$f'(x)=\lim_{h \rightarrow 0}\frac{f(x+h)-f(x)}{h}$$
this definition of derivative

anonymous · Answer

no
i'm just finding the derivative using first principles can you help me with that?

myininaya · Answer

so if f(x) isn't 2x then what is f(x)?

myininaya · Answer

was f(x) suppose to be 2x/(x+4) or 2x/(x-4) instead of it being 2x ?

anonymous · Answer

+4

myininaya · Answer

2x/(x+4) ?

anonymous · Answer

yes

myininaya · Answer

well if f(x)=2x/(x+4)
do you know how to find f(x+h)?

anonymous · Answer

just plug it in

myininaya · Answer

yep where the x is

anonymous · Answer

yes but i can't get the real derivative. can you show me the steps? i know the answer is 8/(x+4)^2

myininaya · Answer

$$f'(x)=\lim_{h \rightarrow 0}\frac{\frac{2(x+h)}{x+h+4}-\frac{2x}{x+4}}{h}$$
combine top fractions there 
it is easy if you just use the drunken smiley face method :)
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