Proving $2- \epsilon < y$ for Limit w/ Epsilon

In summary, we are given a function $y=2+\frac{1}{x^2}$ and we need to prove that for any value of $x>\frac{1}{(\epsilon)^{1/2}}$ where $\epsilon>0$, the inequality $2-\epsilon < y < 2+\epsilon$ holds. This can be shown by first proving $2+\frac{1}{x^2}<2+\epsilon$ and then using the fact that for any value of $x$ and $\epsilon>0$, $y>2>2-\epsilon$.
  • #1
Dethrone
717
0
Suppose we are given the function $y=2+\frac{1}{x^2}$. Prove that given $x>\frac{1}{(\epsilon)^{1/2}}$, where $\epsilon > 0$, then $2- \epsilon < y < 2 + \epsilon$.
So the first part is easy:
$$x>\frac{1}{(\epsilon)^{1/2}}$$
$$x^2>\frac{1}{\epsilon}$$
$$\frac{1}{x^2}<\epsilon$$
$$2+\frac{1}{x^2}<2+\epsilon$$

Now, any hints as to how to prove $2-\epsilon < y$? (Wondering)
 
Mathematics news on Phys.org
  • #2
Rido12 said:
Suppose we are given the function $y=2+\frac{1}{x^2}$. Prove that given $x>\frac{1}{(\epsilon)^{1/2}}$, where $\epsilon > 0$, then $2- \epsilon < y < 2 + \epsilon$.
So the first part is easy:
$$x>\frac{1}{(\epsilon)^{1/2}}$$
$$x^2>\frac{1}{\epsilon}$$
$$\frac{1}{x^2}<\epsilon$$
$$2+\frac{1}{x^2}<2+\epsilon$$

Now, any hints as to how to prove $2-\epsilon < y$? (Wondering)

For any value of x and for any value of $\varepsilon > 0$ is ...

$\displaystyle y > 2 > 2 - \varepsilon\ (1)$

Kind regards

$\chi$ $\sigma$
 

FAQ: Proving $2- \epsilon < y$ for Limit w/ Epsilon

What does it mean to prove $2-\epsilon < y$ for a limit with epsilon?

Proving $2-\epsilon < y$ for a limit with epsilon means showing that for any small value of $\epsilon$, we can find a corresponding value of $y$ that satisfies the inequality. This is important in limit proofs because it helps us demonstrate that the limit exists and is equal to a specific value.

Why is proving $2-\epsilon < y$ necessary in limit proofs?

Proving $2-\epsilon < y$ is necessary in limit proofs because it allows us to show that the limit exists and is equal to a specific value, rather than just approaching a value. This is important in analyzing the behavior of functions and determining their properties.

How do you prove $2-\epsilon < y$ for a limit with epsilon?

To prove $2-\epsilon < y$ for a limit with epsilon, we use the definition of a limit, which states that for any $\epsilon > 0$, there exists a $\delta > 0$ such that if $0 < |x-c| < \delta$, then $|f(x)-L| < \epsilon$. We manipulate this definition to show that $y = L + \epsilon$ satisfies the inequality $2-\epsilon < y$, thus proving the limit.

Can you give an example of proving $2-\epsilon < y$ for a limit with epsilon?

For example, let's say we want to prove that $\lim_{x \to 2} x^2 = 4$. We start by assuming that $0 < |x-2| < \delta$, and we want to show that $|x^2 - 4| < \epsilon$. We can manipulate the latter inequality to get $|x^2 - 4| = |x-2||x+2| < \delta|x+2|$. Since we want the value of $x$ to be close to 2, we can choose $\delta < 1$, which means $1 < x+2 < 3$. Therefore, $|x+2| < 3$. Now, if we choose $\delta < \frac{\epsilon}{3}$, we have $0 < |x-2| < \delta < \frac{\epsilon}{3}$ and $|x+2| < 3$. This means $|x^2 - 4| < \delta|x+2| < \frac{\epsilon}{3} \cdot 3 = \epsilon$. Hence, we have proven $2-\epsilon < y$ for the limit $\lim_{x \to 2} x^2 = 4$.

What are the key steps in proving $2-\epsilon < y$ for a limit with epsilon?

The key steps in proving $2-\epsilon < y$ for a limit with epsilon are: (1) Manipulate the limit definition to get an expression that involves $|x-c|$ and $|f(x)-L|$. (2) Choose a value for $\delta$ that will make $|x-c| < \delta$ true, based on the given value of $\epsilon$. (3) Use this value of $\delta$ to show that $|f(x)-L| < \epsilon$. (4) Simplify the expression to show that $2-\epsilon < y$. (5) Conclude the proof by stating that the limit exists and is equal to $y$.

Back
Top