Chapter 12: Problem 19
How many terms are there in the expansion of \((x+y)^{8} ?\)
Short Answer
Expert verified
There are 9 terms in the expansion.
Step by step solution
01
Understanding the Problem
We need to determine the number of terms in the expansion of \((x+y)^8\). This is a binomial expression raised to a power of 8.
02
Applying the Binomial Theorem
The binomial theorem states that \((x+y)^n\) expands into \(\sum_{k=0}^{n} \binom{n}{k} x^{n-k} y^k\). Therefore, the expansion will have terms for each \(k\) from 0 to \(n\).
03
Counting the Terms
The number of terms in the expansion corresponds to the number of different powers \(k\) can take, which is from 0 to \(n\). Thus, there are \(n+1\) terms.
04
Calculating the Number of Terms
Since \(n=8\) in \((x+y)^8\), plug this into the formula from Step 3. Therefore, the number of terms is \(8+1=9\).
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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 powerful mathematical tool that allows us to expand expressions that are in the form of a binomial, such as \((a + b)^n\). It provides a formula that breaks down these expressions into separate terms, making calculations much simpler.
For \((x + y)^n\), the binomial theorem states:
For \((x + y)^n\), the binomial theorem states:
- Each term in the expansion is determined by the binomial coefficients \(\binom{n}{k}\), which are also known as "combinations."
- The expression \((x + y)^n\) expands to: \[\sum_{k=0}^{n} \binom{n}{k} x^{n-k} y^k\]
- Every term corresponds to a different value of \(k\), from 0 up to \(n\).
Polynomial Expansion
Polynomial Expansion involves breaking down expressions into sums of simpler powers. When we speak about the polynomial expansion of \((x+y)^8\), it refers to expressing it as a sum of terms involving powers of \(x\) and \(y\).
Here's what happens:
Here's what happens:
- In \((x+y)^8\), starting from \( (x+y)^1 = x + y\), multiplying the expression by itself repeatedly generates terms like \(x^8, \; x^7y, \; x^6y^2,\) and so forth.
- Each term has a format where the exponents on \(x\) and \(y\) add up to 8, for example \(7+1,\; 6+2,\; \ldots\).
Combinatorics
Combinatorics, the branch of mathematics dealing with counting and arrangements, plays a central role in understanding polynomial expansions through the binomial theorem.
Why is it important?
Why is it important?
- It helps us determine how many terms the expansion of \((x+y)^n\) has by using the "combinations" principle, seen in the theorem's coefficients.
- For instance, in \((x+y)^8\), using combinatorics, we calculate that there are 9 different combinations or terms, which correspond to the number of ways we can pick \(k\) elements from 8 (ranging \(k\) from 0 to 8).
- Combinatorics not only aids in expansions but also answers broader questions involving arrangements, such as determining possible outcomes in probability.
- The concept of \(\binom{n}{k}\) becomes more than just a term; it’s about understanding the possibilities and choosing functions within any set.