241.19 the e d definition of a limit.

In summary, in order to prove the statement using the $\epsilon,\delta$ definition of a limit, we need to find a value of $\delta$ that satisfies the condition $0<|x-1|<\delta$ and ensures that $\left|\dfrac{2+4x}{3}-2\right| <\epsilon$. This can be achieved by setting $\delta = \dfrac34\epsilon$.
  • #1
karush
Gold Member
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prove the statement using the $\epsilon,\delta$ definition of a limit.
$$\lim_{{x}\to{1}}\frac{2+4x}{3}=2$$
so then
$$x_0=1\quad f(x)=\frac{2+4x}{3}\quad L=2$$
now
$$0<|x-1|<\delta\quad\text
{and}\quad\left|\frac{2+4x}{3}-2\right|
<\epsilon$$
then
$$\left|\frac{2+4x}{3}-\frac{6}{3}\right|=\left|\frac{4x-4}{3}\right|$$
$$=\frac{4}{3}|x-1|=|x-1|<\frac{3}{4}\epsilon$$
finally
$$\left|\frac{2+4x}{3}-2\right|
=\frac{4}{3}|x-1|<\frac{4}{3}\delta
=\frac{4}{3}\left(\frac{3}{4}\epsilon\right)
=\epsilon.$$
 
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  • #2
karush said:
prove the statement using the $\epsilon,\delta$ definition of a limit.
$$\lim_{{x}\to{1}}\frac{2+4x}{3}=2$$
so then
$$x_0=1\quad f(x)=\frac{2+4x}{3}\quad L=2$$
now
$$0<|x-1|<\delta\quad\text
{and}\quad\left|\frac{2+4x}{3}-2\right|
<\epsilon$$
That last statement should read
Given $\epsilon>0$, we need to find $\delta>0$ such that $\left|\dfrac{2+4x}{3}-2\right| <\epsilon$ whenever $0<|x-1|<\delta$.​
karush said:
then
$$\left|\frac{2+4x}{3}-\frac{6}{3}\right|=\left|\frac{4x-4}{3}\right|$$
$$=\frac{4}{3}|x-1|$$
That calculation should then continue $$\left|\frac{2+4x}{3}-\frac{6}{3}\right|=\left|\frac{4x-4}{3}\right|$$
$$=\frac{4}{3}|x-1| < \frac43\delta.$$ In order for that to be less than $\epsilon$, we can take $\delta = \dfrac34\epsilon.$

So your solution is essentially correct, but the wording needs to be clarified.
 

FAQ: 241.19 the e d definition of a limit.

What is the definition of a limit?

The definition of a limit, as given by 241.19 the e d, is the value that a function approaches as the input value approaches a specific point.

How is the limit of a function calculated?

The limit of a function can be calculated by plugging in values closer and closer to the specific point and seeing what value the function approaches.

What is the purpose of finding the limit of a function?

The limit of a function helps us understand the behavior of the function at a specific point and can be used to determine continuity and differentiability.

Can a function have multiple limits?

Yes, a function can have multiple limits depending on the direction from which the input value approaches the specific point. These are known as the left-hand and right-hand limits.

What is the difference between a limit and a value of a function?

The limit of a function represents the behavior of the function at a specific point, while the value of a function represents the output of the function at that specific point.

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