Olympiad corner #2

Q1Q1 Find the largest y such that

11+x2yxy+xforallx>0\frac { 1 }{ 1+{ x }^{ 2 } } \ge \frac { y-x }{ y+x } \quad for\quad all\quad x>0

Q2Q2 Find the minimum and maximum values of

x+1xy+x+1+y+1yz+y+1+z+1zx+z+1\frac { x+1 }{ xy+x+1 } +\frac { y+1 }{ yz+y+1 } +\frac { z+1 }{ zx+z+1 }

#Inequalities #RMO #INMO

Note by Satyajit Ghosh
5 years, 7 months ago

No vote yet
1 vote

  Easy Math Editor

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

  • Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
  • Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
  • Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.
  • Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold

- bulleted
- list

  • bulleted
  • list

1. numbered
2. list

  1. numbered
  2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1

paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
    # 4 spaces, and now they show
    # up as a code block.

    print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in \( ... \) or \[ ... \] to ensure proper formatting.
2 \times 3 2×3 2 \times 3
2^{34} 234 2^{34}
a_{i-1} ai1 a_{i-1}
\frac{2}{3} 23 \frac{2}{3}
\sqrt{2} 2 \sqrt{2}
\sum_{i=1}^3 i=13 \sum_{i=1}^3
\sin \theta sinθ \sin \theta
\boxed{123} 123 \boxed{123}

Comments

Log in to reply

@Satyajit Ghosh Thank you for mentioning me!

A Former Brilliant Member - 5 years, 7 months ago

Applying componendo and dividendo we get 2+x2x22y2x\frac{2+x^{2}}{-x^{2}}\geq\frac{2y}{-2x}

2x+xy\frac{2}{x}+x \geq y

Applying A.MG.MA.M-G.M

2x+x22\frac{2}{x}+x\geq 2\sqrt{2}

Therefore y=22y=2\sqrt{2}.

Shivam Jadhav - 5 years, 7 months ago

Log in to reply

Thanks. How could I forget to tag you! Btw can you even have a look at Olympiad corner#1 q1

Satyajit Ghosh - 5 years, 7 months ago

Log in to reply

Answered

Shivam Jadhav - 5 years, 7 months ago

Log in to reply

@Shivam Jadhav He is asking for question 1 solution. 2nd was easy.

Kushagra Sahni - 5 years, 6 months ago

@Shivam Jadhav What about 2nd question?

Satyajit Ghosh - 5 years, 6 months ago

Lol both questions are Q1?

Kushagra Sahni - 5 years, 7 months ago

Log in to reply

I've fixed it.

Abdur Rehman Zahid - 5 years, 7 months ago

Do u think the 2nd question is correct? Check the expression again from your book.

Kushagra Sahni - 5 years, 7 months ago

Log in to reply

Sorry the denominator of 1st term had xy+y+1 but now I have updated it it to the correct question

Satyajit Ghosh - 5 years, 7 months ago

If you have got the answer, please give a hint at least

Satyajit Ghosh - 5 years, 7 months ago

  1. Cross multiplying we get y+xyx1+x2\dfrac{y+x}{y-x} \ge 1+x^{2} or 2yxx\dfrac{2}{y-x} \ge x or x2yx+20x^{2}-yx+2 \le 0.
This is a quadratic equation in xx and since it is 0\le 0, the discriminant i.e. y28y^{2}-8 must also be 0\le 0 or y8y \le \sqrt {8}.

Therefore, the maximum value of yy is 8\sqrt {8}

A Former Brilliant Member - 5 years, 7 months ago

Log in to reply

Thanks! Can you tell the answer for q2. Do check out my Olympiad corner#1 which has q1 unanswered.

Satyajit Ghosh - 5 years, 7 months ago
×

Problem Loading...

Note Loading...

Set Loading...