# Inequalities ,my weak sense !

1. Dec 18, 2009

### calios

1. The problem statement, all variables and given/known data

hy guys ,help me

prove if x<y and n is odd ,then xn<yn
i have solved this . .but a question in below

2. Relevant equations

3. The attempt at a solution

if 0=or<x<y then xn<yn (i have proved this ) and if x<y<or=0 we can say 0=or<-y<-x it implies -yn<-xn last we can add both side with +xn and +yn we have xn<yn ..
is proved is correct ? and what about if x<y<or=0 ( n is even ) how to prove this ?

thanx before ^_^

2. Dec 18, 2009

### ystael

This is correct, or you can also use the fact that multiplying by $$-1$$ reverses inequalities, i.e., if $$A < B$$ then $$-B < -A$$.

You are missing the case where $$x < 0 < y$$.

In this case, the correct statement is different; try some values for $$x$$ and $$y$$, and you should see what it is.

3. Dec 18, 2009

### Staff: Mentor

You don't need to prove the statement for even n. The statement you're trying to prove explicitly says that n is odd.

4. Dec 19, 2009

### calios

yes ,thanx for correcting :tongue:

5. Dec 19, 2009

### jegues

Couldn't you prove these by the process of mathematical induction as well :3 ?