Mathematical induction inequality

[Julia Maria]

Homework Statement

Prove; n^2 > n+1 for n = 2,3,4 by Induction

Homework Equations

The Attempt at a Solution

p(n)= P(2) 2^2> 2+1 --> 4>3

Induction step:
P(n+1): (n+1)^2 > (n+1) +1
(n+1)^2> n+2
n^2 + 2n + 1 > n+2 | -n
n^2 +n + 1> 2 | -1
n^2 +n > 1

Is this correct, and how do I go from here?

 

[dirk_mec1]

Hint: for what n is the inequality suppose to be valid?

 

[Julia Maria]

For n>1. But I Still struggle to get further..

 

[Mentallic]

You're now supposed to apply your assumption that n^2>n+1 is true. If we know that n^2>n+1 then is n^2+n>1 ?

 

[HallsofIvy]

Homework Statement

Prove; n^2 > n+1 for n = 2,3,4 by Induction

Homework Equations

The Attempt at a Solution

p(n)= P(2) 2^2> 2+1 --> 4>3

Better said "for n= 2, n^2= 2^2= 4> 3= 2+ 1"

Induction step:

You have to first say "assume that for some n, n^2> n+1".
(Personally I prefer to use another letter, k, say, so as not to confuse it with the general n.

P(n+1): (n+1)^2 > (n+1) +1

No, You are asserting what you want to prove.
Instead look at just the left side: (n+1)^2= n^2+ 2n+ 1.
By the "induction hypothesis", n^2> n+ 1 so (n+1)^2> (n+1)+ 2n+ 1= 3n+ 2> n+ 2= (n+1)+1

(n+1)^2> n+2
n^2 + 2n + 1 > n+2 | -n
n^2 +n + 1> 2 | -1
n^2 +n > 1

Is this correct, and how do I go from here?