Proof by Induction - Inequalities

In summary, the conversation is about proving an inequality by induction. The first person asks for confirmation on their solution and the second person points out that the method used is incorrect. They suggest starting from the desired form and transforming it back to the given inequality. The third person provides a helpful hint and points out an error in the solution. The conversation ends with the first person thanking everyone for their help.
  • #1
odolwa99
85
0

Homework Statement



Prove by induction that: (Please see attachment)

Homework Equations



The Attempt at a Solution



Can someone please confirm if I have worked the question out correctly. Many thanks.
 

Attachments

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  • #2
Your method is not correct. Start from the inequality you supposed to be true (for n=k) and transform it till you arrive to the desired form. You started from the case n=k+1 and went backwards. That is wrong. ehild
 
  • #3
It might help you to note that
[tex]\frac{1}{(1+r)^n}\le \frac{1}{1+ rn}[/tex]
is exactly the same as
[tex]1+ rn\le (1+ r)^n[/tex]
so you don't have to worry about the fractions.
 
  • #4
the second line from the end looks incorrect.
[itex]\frac{1}{k\cdot r^2} \le 0 \Leftrightarrow k<0, r\ne 0[/itex]
why won't you try to attack it from another aspect. for example,
[itex]p_1>p2>0 \rightarrow \frac{1}{p_2}>\frac{1}{p_1}[/itex]
 
  • #5
Thank you for the help guys. I genuinely appreciate it.
 

Related to Proof by Induction - Inequalities

What is proof by induction?

Proof by induction is a mathematical method used to prove that a statement is true for all natural numbers. It involves breaking the statement down into smaller cases and proving that it holds true for the first case. Then, assuming it holds true for the nth case, it is proven to hold true for the (n+1)th case. This process is repeated until the statement is proven to hold true for all natural numbers.

What are the steps for using proof by induction?

The steps for using proof by induction are:

  1. Prove the statement for the first case (often n=1).
  2. Assume the statement holds true for the nth case.
  3. Prove that the statement also holds true for the (n+1)th case.
  4. Conclude that the statement is true for all natural numbers.

What is the role of inequalities in proof by induction?

Inequalities are often used in proof by induction to show that a statement holds true for a smaller case, and then use that information to prove that it holds true for a larger case. This allows for a more efficient and concise proof. Inequalities can also be used to show that a statement is true for all natural numbers, rather than just a specific value.

How do you know when to use proof by induction for inequalities?

Proof by induction is typically used for proving statements that involve natural numbers, sequences, and series. If a statement involves inequalities and the variable is a natural number, then proof by induction is a good method to use. Additionally, if the statement seems to have a pattern or is a generalization of a specific case, proof by induction may be a good approach.

What are the common mistakes made when using proof by induction for inequalities?

Some common mistakes made when using proof by induction for inequalities include:

  • Not proving the statement for the first case (n=1).
  • Assuming the statement holds true for the (n+1)th case without first proving it for the nth case.
  • Using incorrect or incomplete algebraic manipulations in the proof.
  • Not stating the base case or inductive hypothesis clearly.
  • Not properly concluding that the statement is true for all natural numbers after completing the proof.

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