For questions about mathematical induction, a method of mathematical proof. Mathematical induction generally proceeds by proving a statement for some integer, called the *base case*, and then proving that if it holds for one integer then it holds for the next integer. This tag is primarily meant ...

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Why are two base cases needed to prove that $n<2^n$ for all $n\geq 0\,$?

So I understand more than one base case is needed when there is a recurrence relation like the Fibonacci sequence. But I don't understand why two base cases are needed in the below example. Is there ...
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1answer
29 views

Proving by induction on the number of vertices that: every acyclic simple graph is bipartite

as my title says, I need to prove that every acyclic simple graph is bipartite, by the use of induction. I have quite some trouble with induction, so hopefully you guys can help me out. :)
2
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2answers
95 views

Why General Leibniz rule and Newton's Binomial are so similar?

The binomial expansion: $$(x+y)^{n} = \sum_{k=0}^{n} \binom{n}{k} x^k y^{n-k}$$ The General Leibniz rule (used as a generalization of the product rule for derivatives): $$(fg)^{(n)} = ...
4
votes
4answers
86 views

Prove $\sum_{i=2}^{n}\frac{1}{(n-1)n}$ = $\frac{(n-1)}{n}$ using induction.

I need to prove $\sum_{i=2}^{n}\frac{1}{(i-1)i}$ = $\frac{(n-1)}{n}$ using induction. I am getting stuck midway through the inductive step. Here is what I have: $\forall n\geq 2$, where ...
3
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4answers
55 views

How to prove $ \sum\limits_{k=1}^{n}\frac{k}{(k+1)!}=1-\frac{1}{(n+1)!}$ using induction?

This is as far as I get. I get stuck here because both sides to not equal each other, but I am not sure what I am doing wrong. $$ \sum\limits_{k=1}^{n}\frac{k}{(k+1)!}=1-\frac{1}{(n+1)!}$$ Assume: ...
0
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1answer
28 views

context-free languages operation closure

The following operation is defined on formal languages. $ operation1(L) = \lbrace w \ | \ wxy \in L, \ \forall x \forall y \ (|x|=|w|) \ \wedge (|y| = |w| ) \rbrace $ Prove that context-free ...
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4answers
60 views

Solution verification: Prove by induction that $a_1 = \sqrt{2} , a_{n+1} = \sqrt{2 + a_n} $ is increasing and bounded by $2$

I have the following recursive relation (sequence): \begin{align} a_1 = \sqrt{2}, \quad a_{n+1} = \sqrt{2 + a_n} \end{align} My Try: I'm a little skeptical of my manipulations near the end but it ...
29
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4answers
2k views

Avoiding proof by induction

Proofs that proceed by induction are almost always unsatisfying to me. They do not seem to deepen understanding, I would describe something that is true by induction as being "true by a technicality". ...
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4answers
57 views

Proving by induction that $n^2 - 7n - 2$ is divisible by $2$

Now proving by induction is fairly simple. However, this is a multiple choice problem whose answers don't make any sense to me. The actual problem goes as follows: To prove by induction that $n^2 - ...
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1answer
26 views

Prove by induction $n^{1/n} ≤ \frac{n+1}{2}$

The problem Prove by induction: $n^{1/n} ≤ \frac{n+1}{2}$ Attempt at solution I started off with the usual steps for an MI problem. We start with the $P_1$ case: for $P_1$, LHS = 1 and RHS = 1 ...
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2answers
55 views

Union-closed families of sets (A problem about induction)

$A$ and $B$ are two sets If $A,B \in F,$ then $A \cup B \in F$. Prove by induction that this property applies to a countable number of sets. If $A_i \in F,i \in \mathbb{N}$, then $ ...
1
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1answer
24 views

How can i prove using induction that the Hadamard matrices are orthogonal?

I can't figure out how to prove using induction that the dot product of 2 rows in a Hadamard matrix is 0. I've always thought of it as just a property of the type of matrix.
2
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1answer
34 views

Use Induction to Show $(1+a)^n \ge 1 + na$

If $a$ $\in$ $\mathbb R$ $\ni$ $a > -1$, then ($\forall n$ $\in$ $\mathbb R$) ($(1+a)^n \ge 1 + na$) My main concern is twofold: Firstly, I am concerned that constant $a$ in the proposition may ...
1
vote
1answer
35 views

Proof of Newton Girard formula symmetric polynomials

Newton Girard formula states that for $k>2$: \begin{equation} p_k=p_{k-1}e_1-p_{k-2}e_2+\cdots +(-1)^{k}p_1e_{k-1}+(-1)^{k+1}ke_{k} \end{equation} where $e_i$ are elementary symmetric functions and ...
0
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3answers
49 views

Proof By Induction $2^n \ge n^2$ for $n\ge4$

I am trying to prove the following, and here is what I have done: Can somebody help to complete this? $2^n \ge n^2$ for $n\ge 4$ $n=4$, LHS: $2^4 = 16$, RHS: $4^2=16$, $16=16$ Therefore TRUE Assume ...
58
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6answers
6k views

Induction on Real Numbers

One of my Fellows asked me whether total induction is applicable to real numbers, too ( or at least all real numbers ≥ 0) . We only used that for natural numbers so far. Of course you have to change ...
2
votes
2answers
31 views

Proof By Induction $n^2 > 3n$ where $n\ge 4$

I am trying to prove the following example, however I seem to be getting a little stuck: For $n\in\mathbb N$, $n\ge 4, n^2>3n$ What I have Done: Base Case:$ n=4$, LHS: $4^2 = 16$, RHS: $3\cdot 4 ...
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votes
2answers
93 views

Prove that $\forall n > 1 \quad2^n - 1 \pmod n \neq 0$

Prove that $\forall n > 1, \quad2^n - 1 \pmod n \neq 0$ I've thought of the induction but I can't figure out how to prove the step. Fermat's theorem (and its variations) aren't particularly useful ...
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1answer
36 views

Proving $2n-8<n^2-8n+14$ for all $n\geq 7$ by induction

For what values of the natural number $n$ is $2n-8 < n^2-8n+14$? (must use induction) I have determined that $n$ appears to work for all values except $n=4,5,6$. I was wondering if this proof ...
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5answers
54 views

Mathematical Induction on a Subset of the Natural Numbers

I am given a strict inequality of the form $$ 2n - 8 < n^2-8n+14, $$ where $n$ belongs to the set of natural numbers $\mathbb{N}$ (in this case $n$ does not equal 0). I am asked, for what values ...
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4answers
66 views

Prove that for all positive integers $n$, $2^1+2^2+2^3+…+2^n=2^{n+1}-2$ [duplicate]

I want to prove that for all positive integers $n$, $2^1+2^2+2^3+...+2^n=2^{n+1}-2$. By mathematical induction: 1) it holds for $n=1$, since $2^1=2^2-2=4-2=2$ 2) if $2+2^2+2^3+...+2^n=2^{n+1}-2$, ...
0
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2answers
57 views

Explaining why proof by induction works [duplicate]

I am learning math proofs for the first time. So I cannot discern the reason for all the details in a proof. Here's the statement of mathematical induction: For every positive integer $n$, let ...
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2answers
25 views

Proof by induction of the Inequality of Harmonic numbers: $H_{2^n} \ge 1+ \frac n2$

My question is, for the question below, in the inductive step, where does $\dfrac{1}{2^{(k+1)}}$ come from?And where does $2^k$ come from in the third last step?
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4answers
58 views

Proving $2^n -1 = \sum_{i=0} ^{n-1} 2^i$ for all $n\geq 1$ by induction

I'm practicing proofs by induction, and equalities seem to be the toughest for me. Can somebody please help to prove that for all integers $n \geq 1$: $$ 2^n -1 = \sum \limits _{i=0} ^{n-1} 2^i\;? $$ ...
1
vote
1answer
32 views

How many comparisons does it take to find a number in a grid of numbers arranged in an $N \times N$ square

We have an $N \times N$ squares, filled with integer numbers monotonically increasing in "right" and "down" directions. So from any point, if you move left the number will get bigger, or if you go ...
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5answers
72 views

Mathematical induction [duplicate]

Prove that $9$ divides $n^3 + (n+1)^3 + (n+2)^3$ where $n$ is a nonnegative integer. I have seen many questions on this site that contain the answer to this problem and I already know the solution, ...
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3answers
35 views

Proof by induction. how can I solve?

How can I demonstrate this equality: $$1+2q+3q^2...+nq^{n-1}=\frac{1-(n+1)q^n+nq^{n+1}} {(1-q)^2} $$ My attempt: if $n=1$ $$1=\frac{1-2q+q^2} {(1-q)^2}=1$$ Now i demonstrate this equality: ...
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5answers
96 views

Proving $9$ divides $n^3 + (n+1)^3 + (n+2)^3$ [duplicate]

I'm trying to prove by MI. I have already distributed n+1, but now I'm stuck on how I can show 9 divides the RHS since $42n$ and $3n^3$ does not divide evenly. ...
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3answers
403 views

Mathematical induction prove that 9 divides $n^3 + (n+1)^3 + (n+2)^3$ . [duplicate]

How can I use mathematical induction to prove that $9$ divides $n^3 + (n+1)^3 + (n+2)^3$ whenever $n$ is a nonnegative integer?
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5answers
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Simple Proof by induction: “9 divides $n^3 + (n+1)^3 + (n+2)^3$”

I'm trying to prove using induction that 9 divides $n^3 + (n+1)^3 + (n+2)^3$ whenever $n$ is a non-negative integer. So far, I have: Base case: P(1) = (1) + (8) + (27) = 36, 36 can be divided by 9 ...
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1answer
20 views

How to prove this proposition with induction

Let $P(x)$ be a polynomial of degree $n$ in the field $\mathbb{R}$ such that $a_n,\ldots,a_0$ are the coefficients. How can I show through induction that if there is at least one coefficient $a_i$ ...
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5answers
88 views

Prove by mathematical induction: $\frac{1}{n}+\frac{1}{n+1}+\dots+\frac{1}{n^2}>1$

Could anybody help me by checking this solution and maybe giving me a cleaner one. Prove by mathematical induction: $$\frac{1}{n}+\frac{1}{n+1}+\dots+\frac{1}{n^2}>1; n\geq2$$. So after I check ...
4
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5answers
100 views

Proving $6^n - 1$ is always divisible by $5$ by induction

I'm trying to prove the following, but can't seem to understand it. Can somebody help? Prove $6^n - 1$ is always divisible by $5$ for $n \geq 1$. What I've done: Base Case: $n = 1$: $6^1 - 1 = ...
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4answers
68 views

Proof by Induction $3^n > n^3$

I am trying to prove the following, however I'm stuck at the Induction hypothesis Prove by induction that, for all integers $n$, if $n\geq 5$, then $3^n>n^3$ What I have Done: Base Case: $n ...
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1answer
42 views

How can I prove by mathematical induction that $\sum_{i=0}^n i^4 = (\sum_{i=0}^n i)^3$?

How can I prove by mathematical induction that $$\sum_{i=0}^n i^4 = (\sum_{i=0}^n i)^3$$ ? I see easily that it holds for $i=0$. Using the inductive hypothesis, I get: $$\sum_{i=0}^{n+1} i^4 = ...
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2answers
42 views

Multiple part problem concerning the proof that $\sum_{k=1}^n k^3=\left(\frac{n(n+1)}{2}\right)^2$ by induction

So I'm having trouble with $c,d$ and $e$. For $c$ so far I have: Inductive Hypothesis: $(\frac{n(n+1)}{2})^2 = (\frac{(k+1)(k+2)}{2})^2$ is that correct?
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Proving $10^n \equiv 1 \pmod 3$ for all $n\geq 1$ by induction

Prove that $10^n \equiv 1 \pmod 3$ for all positive integers $n$ by mathematical induction. Can someone please help me in solving this problem and explain what's going on? Any guidance would be ...
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3answers
79 views

Proving that $2^n+1\leq 3^n$ by induction

I need to prove the following using mathematical induction: $$2^n+1\leq 3^n\qquad\forall n\in\Bbb{Z^+}$$ Been working on this problem for a while and cannot figure it out. Any guidance or help would ...
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5answers
66 views

How to Prove with Mathematical Induction $3^n > n^2$

How do I prove that $3^n > n^2$ with mathematical induction? I thought I had the correct answer but my teacher says its wrong. I let $n=1$ for the initial case and it works. I then assumed $n=k$ ...
0
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1answer
55 views

Where to make induction?

I have read a exercise that states as follows; Use induction to prove that $\forall n \in \mathbb{N}: \forall m \in \mathbb{N}: n<m \Rightarrow \exists r \in \mathbb{N}: n+r=m.$ Sugestion. ...
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4answers
201 views

Prove by strong induction that $2^n$ divides $p_n$ for all integers n ≥ 1 [duplicate]

Let $p_1 = 4$, $p_2 = 8$, and $p_n = 6p_{n−1} − 4p_{n−2}$ for each integer $n ≥ 3$. Prove by strong induction that $2^n$ divides $p_n$ for all integers $n ≥ 1$ I got up to the base step where ...
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1answer
357 views

Proof by induction involving fibonacci numbers

The Fibonacci numbers are defined as follows: $f_0=0$, $f_1=1$, and $f_n=f_{n−1}+f_{n−2}$ for $n≥2$. Prove each of the following three claims: (i) For each $n≥0$, $f_{3n}$ is even. (ii) For each ...
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2answers
29 views

Prove ${4n \choose 2n} = {\frac{1\cdot3\cdot5\cdots(4n-1)}{(1\cdot3\cdot5\cdots(2n-1))^{2}}}{2n \choose n}$

Prove that prove $\dbinom{4n}{2n} = \dfrac{1\cdot3\cdot5\cdots(4n-1)}{(1\cdot3\cdot5\cdots(2n-1))^2} \dbinom{2n}{n}$ using mathematical induction. I have looked all over the internet, been able to ...
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1answer
54 views

basic mathematical induction problem

Prove that for some $b \in \mathbb{N}$, $(\sqrt{2})^n > n$ for every $n \geq b$ Find such a $b \in \mathbb{N}$. Prove that $\forall$$n \geq b$, $(\sqrt{2})^n > n$ How would I approach ...
2
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2answers
94 views

Show that $f(x)=0$ for all $x \in [a,b]$.

I have the following problem: Suppose that $f$ is continuous on $[a,b]$ and suppose that for all $x \in [a,b]$, $f(x) \geq 0$ and $f(x)\leq \int_a^x f(t)dt$. Show that $f(x)=0$ for all $x \in ...
5
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3answers
703 views

Proof by induction of Bernoulli's inequality: $(1 + x)^n \geq 1 + nx$

I'm asked to used induction to prove Bernoulli's Inequality: If $1+x>0$, then $(1+x)^n\geq 1+nx$ for all $n\in\mathbb{N}$. This what I have so far: Let $n=1$. Then $1+x\geq 1+x$. This is true. Now ...
3
votes
5answers
142 views

Prove that $2^n\le n!$ for all $n \in \mathbb{N},n\ge4$

The problem i have is: Prove that $2^n\le n!$ for all $n \in \mathbb{N},n\ge4$ Ive been trying to use different examples of similar problems like at: ...
4
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1answer
59 views

Transfinite Induction in Peano Arithmetic

I have heard that Peano Arithmetic (PA) cannot perform transfinite induction up to $\varepsilon_0$. This seems to imply that it can induct up to smaller ordinals, like $\omega$ or $\omega^\omega$ or ...
2
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1answer
73 views

If there is an injection $f: X \to Y$ with $m=n$ then $f$ is a bijection.

The Statement of the Problem: Let $X,Y$ be finite sets with $ \lvert X \rvert = m $ and $ \lvert Y \rvert = n $. Prove the following statement by induction on $ m \ge 1$: If there is an injection ...
12
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5answers
240 views

Show that $({\sqrt{2}\!+\!1})^{1/n} \!+ ({\sqrt{2}\!-\!1})^{1/n}\!\not\in\mathbb Q$

How could we prove that for every positive integer $n$, the number $$({\sqrt{2}+1})^{1/n} + ({\sqrt{2}-1})^{1/n}$$ is irrational? I think it could be done inductively from a more general ...