Chapter 1: Problem 4
You are given \(\lim _{x \rightarrow a} f(x)=L\) and a tolerance \(\varepsilon\). Find a number \(\delta\) such that \(|f(x)-L|<\varepsilon\) whenever \(0<|x-a|<\delta\) \(\lim _{x \rightarrow-2}(3 x-2)=-8 ; \quad \varepsilon=0.05\)
Short Answer
Expert verified
The short answer is: \(\delta \approx 0.0167\).
Step by step solution
01
Identify the function's limit
We are given that \(\lim_{x \rightarrow -2} (3x - 2) = -8\). This means that as \(x\) approaches \(-2\), the value of the function \((3x - 2)\) approaches \(-8\).
02
Identify the Tolerance
We are given a tolerance \(\varepsilon = 0.05\). This means we want to find a \(\delta\) such that the difference between the function's value and its limit is less than \(0.05\).
03
Write down the condition for \(\delta\)
We need to find a \(\delta\) such that \(|f(x) - L| < \varepsilon\) whenever \(0 < |x - a| < \delta\). In this case, we have:
- \(f(x) = 3x - 2\)
- \(L = -8\)
- \(a = -2\)
- \(\varepsilon = 0.05\)
Thus, we want to find a \(\delta\) such that \(|(3x - 2) - (-8)| < 0.05\) whenever \(0 < |x - (-2)| < \delta\).
04
Simplify the Condition
To simplify the condition, let's first simplify the absolute value expression:
\(|(3x - 2) - (-8)| = |3x - 2 + 8| = |3x + 6|\)
Now the condition becomes:
\(|3x + 6| < 0.05\) whenever \(0 < |x + 2| < \delta\)
05
Find the appropriate \(\delta\)
Now we want to find a \(\delta\) value such that \(|3x + 6| < 0.05\) whenever \(0 < |x + 2| < \delta\). We can reason as follows:
- Since \(|x + 2| < \delta\), we can multiply both sides of the inequality by \(3\) to get \(|3x + 6| < 3\delta\).
- We want \(|3x + 6| < 0.05\), so we can set \(3\delta = 0.05\).
- Solving for \(\delta\), we have \(\delta = \frac{0.05}{3} \approx 0.0167\).
Thus, our desired \(\delta\) value is \(\delta \approx 0.0167\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Epsilon-Delta Definition
The concept of the **epsilon-delta definition** is crucial when understanding limits in calculus. It's all about defining how close we need to be to a particular point. In essence, when we say \( \lim_{x \rightarrow a} f(x) = L \), we mean:
- For every positive number \( \varepsilon \), no matter how small,
- There exists a positive number \( \delta \) such that
- Whenever \( |x - a| < \delta \), it ensures \( |f(x) - L| < \varepsilon \)
Tolerance in Limits
Understanding **tolerance in limits** is about recognizing how much deviation from the limit is acceptable. The value \( \varepsilon \) represents this tolerance.
- It dictates just how close \( f(x) \) needs to get to \( L \).
- A smaller \( \varepsilon \) demands more precision, meaning \( f(x) \) must be even closer to \( L \).
Finding Delta in Limits
**Finding delta in limits** involves determining how closely \( x \) must approach \( a \) to keep \( f(x) \) within the designated \( \varepsilon \) range of \( L \). This critical step ensures our function remains within that "tolerated" difference.
- We identify \( |x - a| < \delta \) which maintains \( |f(x) - L| < \varepsilon \).
- Essentially, \( \delta \) controls the input closeness needed for output precision.
Absolute Value Inequality
Using **absolute value inequality** is a method to express the range within which the function must stay close to the limit. It provides a flexible way of showing proximity both above and below the limit.
- The expression \( |f(x) - L| < \varepsilon \) implies strict bounds around \( L \).
- It's a two-sided inequality handling positive and negative deviations.
Continuity of Functions
The **continuity of functions** reflects the idea that a function should not have abrupt shifts or breaks around a point \( a \). If we have \( \lim_{x \rightarrow a} f(x) = f(a) \), it indicates continuity at point \( a \).
- Continuous functions allow limits to match function values neatly.
- They do not break or jump unexpectedly at \( x = a \).