# Differential calculus problem using limits

### Differential calculus problem using limits

1.a) Use the formal definition of the derivative to compute f'(2) when
$$f(x)=(1-x)/2x$$

1.b) Do the same to find f'(x)
Guest

### Re: differential calculus problem using limits

a) $$f'(2) = \lim_{x \to 2}\frac{f(x) - f(2)}{x-2}=\lim_{x \to 2}\frac{\frac{1-x}{2x}-\frac{-1}{4}}{x-2}=\lim_{x \to 2}\frac{2-x}{4x(x-2)}=\lim_{x \to 2}(-\frac{1}{4x})=-\frac{1}{8}$$
b) f'(x) = $$\lim_{x \to x_{0 }}\frac{f(x) - f(x_{0 }}{x-x_{0 }}=\lim_{x \to x_{0 }}\frac{\frac{1-x}{2x}-\frac{1-x_{0 }}{2x_{0 }}}{x-x_{0 }}=\lim_{x \to x_{0 }}\frac{x_{0 }-x}{2xx_{0 }(x-x_{0 })}=\lim_{x \to x_{0 }}\frac{-1}{2xx_{0}}=-\frac{1}{2x_{0 }^{2}}$$.

nathi123

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Joined: Sun Sep 17, 2017 1:56 pm
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### Re: differential calculus problem using limits

Could you explain the formulas used and why?
Guest

### Re: Differential calculus problem using limits

I use the difinition of the derivative in point ,if y = f(x) $$\Rightarrow y'(x_{0}) = \lim_{x \to x_{0 }}\frac{f(x)-f(x_{0})}{x-x_{0 }}$$

nathi123

Posts: 21
Joined: Sun Sep 17, 2017 1:56 pm
Reputation: 19