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If we wish to expand \((x+y)^{8},\) what is the coefficient of \(x^{5} y^{3} ?\) What is the coefficient of \(x^{3} y^{5} ?\)

Short Answer

Expert verified
Both coefficients are 56.

Step by step solution

01

Identify the Binomial Expansion Formula

The expression \((x+y)^n\) can be expanded using the binomial theorem. The formula is given by: \[(x+y)^n = \sum_{k=0}^{n} \binom{n}{k} x^{n-k} y^{k},\] where \( \binom{n}{k} \) is the binomial coefficient.
02

Recognize the Terms for x^5 y^3 and x^3 y^5

To find the coefficient of a specific term, identify the correct powers for \(x\) and \(y\). For \(x^5 y^3\), use \(n-k = 5\) and \(k = 3\). For the term \(x^3 y^5\), switch these to \(n-k = 3\) and \(k = 5\).
03

Apply the Binomial Coefficient for x^5 y^3

For the term \(x^5 y^3\), calculate the binomial coefficient: \[\binom{8}{3} = \frac{8!}{3!(8-3)!} = \frac{8 \times 7 \times 6}{3 \times 2 \times 1} = 56.\]
04

Apply the Binomial Coefficient for x^3 y^5

Similarly, calculate the binomial coefficient for \(x^3 y^5\): \[\binom{8}{5} = \frac{8!}{5!(8-5)!} = \frac{8 \times 7 \times 6}{3 \times 2 \times 1} = 56.\] Notice that \(\binom{8}{3} = \binom{8}{5}\) because choosing 3 objects from 8 is the same as choosing 5 objects to leave out.

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Key Concepts

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

Binomial Theorem
The Binomial Theorem is a fundamental principle in algebra that provides a powerful way to expand expressions of the form \((x + y)^n\). Using this theorem, we can break down complex expressions into simpler terms. The general formula for the binomial expansion is:
\[(x+y)^n = \sum_{k=0}^{n} \binom{n}{k} x^{n-k} y^{k},\]
where "\(n\)" represents the power to which the binomial is raised, and "\(k\)" indicates the specific term in the expansion. The theorem allows each term of the expansion to have the structure of a product of a binomial coefficient and powers of each binomial element.
  • "\(\binom{n}{k}\)" is the binomial coefficient, a key component in binomial expansion.
  • "\(x^{n-k}\)" and "\(y^{k}\)" represent the powers of the two components inside the binomial.
This theorem is a backbone of combinatorics and algebraic calculations, providing a way to handle polynomial growth in mathematics.
Binomial Coefficient
The Binomial Coefficient, denoted as \(\binom{n}{k}\), represents the number of ways to choose \(k\) items from \(n\) available options without considering the order. It is integral in calculating each term of a binomial expansion, expressing how multiple combinations contribute to coefficients of polynomial terms. The formula for this coefficient is:
\[\binom{n}{k} = \frac{n!}{k!(n-k)!},\]
where "!" (factorial) signifies the product of all positive integers up to that number.
  • For example, \(\binom{8}{3}\) provided the coefficient for \(x^5 y^3\) as well as \(x^3 y^5\).
  • The equality \(\binom{8}{3} = \binom{8}{5}\) highlights the principle that choosing "3" items is the same as choosing "5" to leave out.
This symmetry in binomial coefficients often simplifies calculations and problem-solving in algebra and combinatorics alike.
Combinatorics
Combinatorics is the field of mathematics concerned with counting and arranging objects according to defined rules. It is deeply connected with the binomial theorem and binomial coefficients thanks to its focus on combinations and permutations.
Combinatorics provides tools like the basic principles of counting and ordering.
  • Selection without order: Using binomial coefficients, we explore how objects can be selected if the arrangement doesn't matter (e.g., choosing 3 fruits from a basket of 8, irrespective of which fruits are chosen).
  • Symmetry in choices: As seen with \(\binom{8}{3} = \binom{8}{5}\), combinatorics often reveals symmetry in problems, simplifying computations and understanding.
These techniques are integral to solving complex counting problems not only in mathematics but also in fields like computer science and statistics. They provide insights into how to effectively manage and interpret data.

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Most popular questions from this chapter

The Bureau of the Census reports that the median family income for all families in the United States during the year 2003 was \(\$ 43,318\). That is, half of all American families had incomes exceeding this amount, and half had incomes equal to or below this amount. Suppose that four families are surveyed and that each one reveals whether its income exceeded \(\$ 43,318\) in 2003 . a. List the points in the sample space. b. Identify the simple events in each of the following events: A: At least two had incomes exceeding \(\$ 43,318\). \(B:\) Exactly two had incomes exceeding \(\$ 43,318\) C: Exactly one had income less than or equal to \(\$ 43,318\). c. Make use of the given interpretation for the median to assign probabilities to the simple events and find \(P(A), P(B),\) and \(P(C)\).

Suppose that two defective refrigerators have been included in a shipment of six refrigerators. The buyer begins to test the six refrigerators one at a time. a. What is the probability that the last defective refrigerator is found on the fourth test? b. What is the probability that no more than four refrigerators need to be tested to locate both of the defective refrigerators? c. When given that exactly one of the two defective refrigerators has been located in the first two tests, what is the probability that the remaining defective refrigerator is found in the third or fourth test?

Prove that \(\left(\begin{array}{c}n+1 \\\ k\end{array}\right)=\left(\begin{array}{l}n \\\ k\end{array}\right)+\left(\begin{array}{c}n \\ k-1\end{array}\right).\)

Probability played a role in the rigging of the April 24,1980 , Pennsylvania state lottery (Los Angeles Times, September 8,1980 ). To determine each digit of the three-digit winning number. each of the numbers \(0,1,2, \ldots, 9\) is placed on a Ping-Pong ball. the ten balls are blown into a compartment, and the number selected for the digit is the one on the ball that floats to the top of the machine. To alter the odds, the conspirators injected a liquid into all balls used in the game except those numbered 4 and \(6,\) making it almost certain that the lighter balls would be selected and determine the digits in the winning number. Then they bought lottery tickets bearing the potential winning numbers. How many potential winning numbers were there (666 was the eventual winner)?

A businesswoman in Philadelphia is preparing an itinerary for a visit to six major cities. The distance traveled, and hence the cost of the trip, will depend on the order in which she plans her route. a. How many different itineraries (and trip costs) are possible? b. If the businesswoman randomly selects one of the possible itineraries and Denver and San Francisco are two of the cities that she plans to visit, what is the probability that she will visit Denver before San Francisco?

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