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In Exercises \(11-30,\) use mathematical induction to prove that each statement is true for every positive integer \(n\) $$ 1+3+5+\dots+(2 n-1)=n^{2} $$

Short Answer

Expert verified
The sum of all odd numbers up to \(2n-1\) is equal to \(n^2\) for every positive integer \(n\). This has been proven using mathematical induction, which includes a base case, an induction assumption, and an induction step.

Step by step solution

01

Base Case

Firstly, check if the statement holds true for the base case \(n=1\). \nHere, the left side of the equation is 1 (the first odd number) and the right side of the equation is \(1^2=1\). Therefore, the statement holds true for \(n=1\).
02

Induction Hypothesis

Now, make an induction hypothesis. Assume that the given statement is true for some positive integer \(k>1\), i.e., \(1+3+5+...+(2k-1)=k^2\). The aim is to prove that the statement is also true for \(n=k+1\).
03

Induction Step

Let's prove the statement for \(n=k+1\). If the induction hypothesis is correct, then we can write \((1+3+5+...+(2k-1)+(2(k+1)-1) = (k+1)^2\). \n The left side becomes \(k^2 + 2(k+1)-1\). The right side is \((k+1)^2 = k^2 + 2k +1\). \nBoth the left side and the right side of the equation are equivalent, hence the statement is true for every positive integer.

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Key Concepts

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

Algebra
Algebra is a branch of mathematics dealing with symbols and the rules for manipulating those symbols; it is a language through which we describe patterns and relationships between quantities. In the context of the provided exercise, algebra is employed to discern a pattern in a series of odd numbers.

The task involves showing that the sum of a sequence of odd numbers up to any positive integer can be expressed as a perfect square, specifically, the sum of the odd numbers up to the nth term is equal to the square of n ((n^2)). To embark on this proof requires a solid understanding of algebraic expressions, the ability to simplify and manipulate them, and the recognition of how sequences behave algebraically.

For instance, the series mentioned in the exercise can be algebraically represented using the nth term formula for an arithmetic sequence, where each term after the first can be found by adding a common difference, in this case 2, to the previous term. Thus, the nth odd number in the sequence is (2n - 1). Demonstrating a thorough understanding of algebra is critical to correctly performing and grasping the steps in mathematical induction.
Proofs
Proofs constitute the foundation of mathematical verification and are indispensable for asserting the truth of a mathematical statement beyond any doubt. They come in various forms, such as direct proof, contradiction, contrapositive, and induction, with our current focus being on mathematical induction.

Mathematical induction is a powerful proof technique, particularly suited for proving statements about integers. The exercise at hand utilizes this approach to confirm that a particular rule about the sum of odd numbers applies to all positive integers. Induction involves two crucial steps: verifying a base case, which is the smallest value for which the statement is supposed to hold, and then showing that if the statement holds for an arbitrary integer, it must also hold for the next integer. This second step is the induction step and simulates a domino effect, where the correctness of one instance topples into the correctness of the next.

The beauty of induction lies in its logical elegance and the creative ways it can be applied to a myriad of problems in mathematics.
Sequences and Series
Sequences and series are fundamental concepts in mathematics that involve ordered lists of numbers and their summations, respectively. In algebra, sequences are typically defined by a formula that allows the computation of any term from its position in the sequence. In the exercise, we deal with a simple sequence: the list of odd numbers.

A series is the sum of the terms of a sequence. The exercise we're looking at involves the series of odd numbers, and it challenges us to prove a relationship between this series and square numbers. The nth partial sum of this specific sequence is the sum of the first n terms, which is claimed to be equal to (n^2). This relates the concept of sequences directly to the idea of series, as we're looking at the sum of a sequence's terms and expressing this sum in a simplified form.

Understanding sequences and series is essential for tackling problems in various domains of mathematics, such as calculus, number theory, and even in practical applications like computing interests in finance or understanding patterns in the natural world.

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Most popular questions from this chapter

Write the first three terms in each binomial expansion, expressing the result in simplified form. $$ \left(x^{2}+1\right)^{16} $$

Evaluate the given binomial coefficient. $$ \left(\begin{array}{c}100 \\\98\end{array}\right) $$

Follow the outline on the next page to use mathematical induction to prove that $$ \begin{aligned}(a+b)^{n}=\left(\begin{array}{c}n \\\0\end{array}\right) a^{n}+\left(\begin{array}{c}n \\\1\end{array}\right) a^{n-1} b+\left(\begin{array}{c}n \\\2\end{array}\right) a^{n-2} b^{2} \\\\+\cdots+\left(\begin{array}{c}n \\\n-1\end{array}\right) a b^{n-1}+\left(\begin{array}{c}n \\\n\end{array}\right) b^{n}\end{aligned} $$ a. Verify the formula for \(n=1\) b. Replace \(n\) with \(k\) and write the statement that is assumed true. Replace \(n\) with \(k+1\) and write the statement that must be proved. c. Multiply both sides of the statement assumed to be true by \(a+b .\) Add exponents on the left. On the right, distribute \(a\) and \(b,\) respectively. d. Collect like terms on the right. At this point, you should have $$ \begin{aligned}&(a+b)^{k+1}=\left(\begin{array}{l}k \\\0\end{array}\right) a^{k+1}+\left[\left(\begin{array}{l}k \\\0\end{array}\right)+\left(\begin{array}{l}k \\\1\end{array}\right)\right] a^{k} b\\\&\begin{array}{l}+\left[\left(\begin{array}{c}k \\\1\end{array}\right)+\left(\begin{array}{c}k \\\2\end{array}\right)\right] a^{k-1} b^{2}+\left[\left(\begin{array}{c}k \\\2\end{array}\right)+\left(\begin{array}{c}k \\\3\end{array}\right)\right] a^{k-2} b^{3} \\\\+\cdots+\left[\left(\begin{array}{c}k \\\k-1\end{array}\right)+\left(\begin{array}{c}k \\\k\end{array}\right)\right] a b^{k}+\left(\begin{array}{c}k \\\k\end{array}\right) b^{k+1} \end{array}\end{aligned} $$ e. Use the result of Exercise 74 to add the binomial sums in brackets. For example, because \(\left(\begin{array}{l}n \\\ r\end{array}\right)+\left(\begin{array}{c}n \\\ r+1\end{array}\right)$$=\left(\begin{array}{l}n+1 \\ r+1\end{array}\right),\) then \(\left(\begin{array}{l}k \\ 0\end{array}\right)+\left(\begin{array}{l}k \\\ 1\end{array}\right)=\left(\begin{array}{c}k+1 \\\1\end{array}\right)\) and\(\left(\begin{array}{l}k \\ 1\end{array}\right)+\left(\begin{array}{l}k \\\2\end{array}\right)=\left(\begin{array}{c}k+1 \\ 2\end{array}\right)\) f. Because \(\left(\begin{array}{l}k \\\ 0\end{array}\right)=\left(\begin{array}{c}k+1 \\ 0\end{array}\right) \quad\) (why?) and \(\left(\begin{array}{l}k \\ k\end{array}\right)=\) \(\left(\begin{array}{l}k+1 \\ k+1\end{array}\right)\) (why?), substitute these results and the results from part (e) into the equation in part (d). This should give the statement that we were required to prove in the second step of the mathematical induction process.

Find the term indicated in each expansion. \(\left(x+\frac{1}{2}\right)^{8} ;\) fourth term

Show that $$ \left(\begin{array}{l}n \\\r\end{array}\right)+\left(\begin{array}{c}n \\\r+1\end{array}\right)=\left(\begin{array}{l}n+1 \\\r+1 \end{array}\right) $$ Hints: $$ \begin{aligned}&(n-r) !=(n-r)(n-r-1) !\\\&(r+1) !=(r+1) r !\end{aligned} $$

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