Proof of square root properties

Click For Summary
SUMMARY

The discussion focuses on proving the inequality \(\sqrt{\sum_{i=1}^{n} x_{i}^{2}} \leq \sum_{i=1}^{n} |x_{i}|\) and its relationship to the Cauchy-Schwarz inequality. Participants emphasize the importance of understanding the conditions under which the equality holds and the implications of squaring both sides of the inequality. The conversation highlights the necessity of recognizing cross terms that arise when manipulating the expressions, which are critical for establishing the proof rigorously.

PREREQUISITES
  • Understanding of basic algebraic manipulation
  • Familiarity with inequalities, particularly the Cauchy-Schwarz inequality
  • Knowledge of proof techniques in mathematics
  • Basic concepts of sequences and summations
NEXT STEPS
  • Study the Cauchy-Schwarz inequality in detail
  • Learn about the properties of norms in vector spaces
  • Explore techniques for proving inequalities in mathematics
  • Investigate the implications of squaring inequalities and handling cross terms
USEFUL FOR

Students and educators in mathematics, particularly those focusing on proof-based courses, as well as anyone interested in deepening their understanding of inequalities and mathematical proofs.

diracy
Messages
20
Reaction score
0

Homework Statement


\sqrt{\sum}x^{2}_{i}\leq\sum|x_{i}|\leq\sqrt{n}\sqrt{\sum}x^{2}_{i}

*The sums are all from i=1 to n.*


Homework Equations





The Attempt at a Solution


I'm very new to proof-based math, and just looking for some help to get started with this one. Thanks in advance.
 
Physics news on Phys.org
For this part
\sqrt{\Sum_i x_i^2} \leq \Sum_i |x_i|

it should be clear
0 \leq \sqrt{\Sum_i x_i^2}
0 \leq \leq \Sum_i |x_i|

so squaring both sides could be useful
 
I tried that and didn't get far. It seems to my the leftmost inequality is always equal. I must be thinking about it wrong. In what instance would that inequality be less than?
 
you should some cross terms like |xi||xj| on in the middle, which don't appear on the left
 

Similar threads

Replies
9
Views
1K
  • · Replies 105 ·
4
Replies
105
Views
7K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 24 ·
Replies
24
Views
4K
  • · Replies 7 ·
Replies
7
Views
2K