Proving a/b+b/a >= 2 using Mathematical Proof | Homework Help

Click For Summary

Homework Help Overview

The problem involves proving that the expression a/b + b/a is greater than or equal to 2, where a and b are positive real numbers. This falls under the subject area of inequalities in algebra.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss various approaches, including adding the ratios and analyzing the numerator and denominator separately. Some suggest multiplying through by ab to simplify the expression. Others mention a potential connection to the law of cosines and consider alternative formulas involving squares of a and b.

Discussion Status

The discussion is active, with participants exploring different methods and insights. Some have provided guidance on potential approaches, while others are questioning the relationships between the variables involved. There is no explicit consensus on a single method yet.

Contextual Notes

Participants are working under the constraints of proving the inequality without using specific solutions or methods, which may lead to varied interpretations of the problem.

TheMathNoob
Messages
189
Reaction score
4

Homework Statement


Let a,b be in the positive reals. Prove a/b+b/a is >=2

Homework Equations

The Attempt at a Solution


I have no idea. Maybe add the two ratios: (a^2+b^2)/a*b and then try to analyze separately the numerator and denominator?
 
Physics news on Phys.org
Those a's and b's in the denominator are pesky. Why not multiply through by ab and see what that gives you?
 
jbriggs444 said:
Those a's and b's in the denominator are pesky. Why not multiply through by ab and see what that gives you?
I feel like this is related to the law of cosines
 
TheMathNoob said:
I feel like this is related to the law of cosines
Your powers of pattern recognition are good, but there is another formula involving a2, b2 and 2ab that is simpler yet.
 
jbriggs444 said:
Your powers of pattern recognition are good, but there is another formula involving a2, b2 and 2ab that is simpler yet.
oh hahahahahah (a-b)^2>=0
when a=b (a-b)^2=0
when a!=b (a-b)^2>0
so (a-b)^2>=0
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 3 ·
Replies
3
Views
3K
Replies
12
Views
4K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
Replies
11
Views
3K