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Let \(S\) be a sample space for an experiment, and let \(E\) and \(F\) be events of this experiment. Show that the events \(E \cup F\) and \(E^{c} \cap F^{c}\) are mutually exclusive. Hint: Use De Morgan's law.

Short Answer

Expert verified
Using De Morgan's law \((A \cup B)^c = A^c \cap B^c\), we rewrite the given events and apply the distributive law to find their intersection: \((E \cup F) \cap (E^c \cap F^c) = (E \cap E^c) \cup (F \cap F^c)\). Since \(E \cap E^c = \emptyset\) and \(F \cap F^c = \emptyset\), the intersection is \(\emptyset\), proving that the events \(E \cup F\) and \(E^c \cap F^c\) are mutually exclusive.

Step by step solution

01

Define mutually exclusive events

Mutually exclusive events are events that cannot both occur at the same time. Mathematically, if E and F are mutually exclusive events, then their intersection is an empty set, i.e., \(E \cap F = \emptyset\).
02

Write the given events using set notation

We're given the events \(E \cup F\) and \(E^c \cap F^c\). Using set notation, we can write these events as follows: - Event \(E \cup F\) is the union of sets E and F. - Event \(E^c \cap F^c\) is the intersection of the complements of sets E and F.
03

Apply De Morgan's law

We will use De Morgan's law to rewrite the event \(E^c \cap F^c\). De Morgan's law states that: \((A \cup B)^c = A^c \cap B^c\). In our case, we will set A = \(E^c\) and B = \(F^c\), and then apply the law to obtain: \((E^c \cap F^c)^c = (E^c)^c \cup (F^c)^c\), which simplifies to \(E \cup F = E^c \cap F^c\).
04

Determine the intersection of the events

To show that the events \(E \cup F\) and \(E^c \cap F^c\) are mutually exclusive, we need to determine their intersection: \((E \cup F) \cap (E^c \cap F^c)\).
05

Apply the distributive law

We will use the distributive law to find the intersection: \((E \cup F) \cap (E^c \cap F^c)\). The distributive law states that \(A \cap (B \cup C) = (A \cap B) \cup (A \cap C)\). By setting A = \(E \cup F\), B = \(E^c\), and C = \(F^c\), we obtain the following: \((E \cup F) \cap (E^c \cap F^c) = (E \cap E^c) \cup (F \cap F^c)\).
06

Evaluate the intersection terms

Now, we need to evaluate the intersection terms \((E \cap E^c)\) and \((F \cap F^c)\). Given that \(E^c\) and \(F^c\) are the complements of sets E and F, their intersections with their corresponding sets will always be empty sets or \(E \cap E^c = \emptyset\) and \(F \cap F^c = \emptyset\).
07

Prove the events are mutually exclusive

Due to the intersection terms being empty sets, we can rewrite step 5 as follows: \((E \cup F) \cap (E^c \cap F^c) = \emptyset \cup \emptyset = \emptyset\). Since the intersection of events \(E \cup F\) and \(E^c \cap F^c\) is an empty set, we can now conclude that these events are mutually exclusive.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

De Morgan's Law
Understanding De Morgan's law is crucial when studying set theory and probability.

Simply put, De Morgan's law provides a method for translating sentences involving 'and' into sentences involving 'or', and vice versa when working with sets and their complements. It is expressed in set notation as:
\begin{itemize}\item For any two sets A and B, \( (A \cup B)^c = A^c \cap B^c \) \item Similarly, \( (A \cap B)^c = A^c \cup B^c \)\end{itemize}
This is particularly helpful when we are trying to prove that two events are mutually exclusive or, in other words, cannot occur at the same time as it allows us to understand and manipulate the relationships between sets and their complements. In probability theory, this translates into the complement rule which states that the probability of not occurring is equal to one minus the probability of occurring.

Using De Morgan's law, we can simplify and derive relationships that may not be immediately obvious. For example, if we need to show that two compound events are mutually exclusive, we can use De Morgan's law to rewrite one event in terms of the other, which leads to an easier comparison of the two. It's a tool that simplifies complex relationships and helps prove such concepts more methodically.
Set Notation
In mathematics, especially in probability theory, it is essential to understand set notation as it provides a universal language to describe collections of objects or numbers, referred to as 'sets'.

Here's what you need to know:
\begin{itemize}\item A 'set' is a collection of distinct elements.\item The symbol \(\cup\) denotes the union of two sets, including all elements that are in either of the sets.\item The symbol \(\cap\) represents the intersection of two sets, referring to elements common to both sets.\item The 'complement' of a set, denoted by a superscript \(c\), consists of all elements not in the set.\item An 'empty set', denoted by \(\emptyset\), is a set with no elements.\end{itemize}
When dealing with multiple sets, it's crucial to be able to express relationships, such as union and intersection, clearly. In our exercise example, the concepts of union (\(E \cup F\)) and intersection (\(E^c \cap F^c\)) are vital to demonstrate that two events are mutually exclusive. The use of set notation isn't just about symbols; it represents a powerful language that clarifies the structure and relationships within mathematics.
Probability Theory
Probability theory is the branch of mathematics concerned with the analysis of random phenomena and is fundamental to statistics, finance, gambling, science, and philosophy.

In probability theory, 'events' are outcomes or sets of outcomes from some random process. The 'sample space', denoted \(S\), is the set of all possible events. When we say that events are 'mutually exclusive', we mean that they cannot occur at the same time - the occurrence of one event excludes the others.

The key formulas and concepts in probability theory related to mutual exclusivity include:
\begin{itemize}\item The probability of the union of two mutually exclusive events is the sum of the probabilities of the individual events.\item If the intersection of two events is the empty set (\(E \cap F = \emptyset\)), then these events are mutually exclusive.\end{itemize}
Understanding these foundational concepts is essential for solving problems in probability. By grasping how to apply set notation and concepts like mutually exclusive events, students can navigate complex probability scenarios with greater ease and accuracy.

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