Vieta: An Opera in Two Acts by Andrei Golovanov

Algebra Level 5

A picture of the scene The lights turn on, the curtain opens and Act One of the world-famous opera, Vieta, commences.

"The sum of the roots of 4 x 12 36 x 11 + 3 x 7 + 7 x 2 + 1 = 0 4x^{12}-36x^{11}+3x^7+7x^2+1=0 is A A . Let me introduce performer Gustav von A A !"

Loud round of applause. Gustav von A A sings The Joy of Vieta , by Wolfram Alphaeus Mozart. The curtain drops.

After a short interlude, the curtain reopens to reveal a brightly lit stage. In big letters is written 3 A x 3 3 = 0 3Ax^3-3=0 . Gustav von Schnieber appears to a roar of applause and sings a solo piece in basso: The Product of the Roots of that 'Nomial . He finishes by revealing that number. What was it? (It is a recurring number so just input the first few decimal places. Gustav von Schnieber, however, is still on stage finishing saying it!)


The answer is 0.11111111.

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1 solution

Through all the empty words and unneeded phrasing we have:

A A is the sum of the roots of 4 x 12 36 x 11 + 3 x 7 + 7 x 2 + 1 = 0 4x^{12}-36x^{11}+3x^7+7x^2+1=0 . By Vieta's formula , we know that the sum of the roots is a 12 a 11 = 36 4 = 9 -\frac {a_{12}}{a_{11}}=-\frac {-36}{4}=9 . Therefore we know that A A is 9 9 .

Next, in part two we need to find the product of the roots of 3 A x 3 3 = 0 3Ax^3-3=0 . As we know A A ( 9 ) 9) , we can substitute it in there to get the equation 27 x 3 3 = 0 27x^3-3=0 . Now we simply need to find the product of the roots of that equation. By Vieta (again) we know that it is a 0 a 3 = 3 27 = 0.111 -\frac {a_0}{a_3}=-\frac {-3}{27}=0.111 (to the first few decimal places).

Although I loved the phrasing, I'm still wondering how this is a level 4 question!

Ameya Daigavane - 6 years, 1 month ago

By Vieta's you should get product of the roots as 0.111... and not -0.111... The product of roots of a cubic is the negative of the constant term over the leading coefficient.

vishnu c - 6 years, 1 month ago

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Yes, you are correct. I'll change it now. @vishnu c

A Former Brilliant Member - 6 years, 1 month ago

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Is there a way to change the answer to a question once you've published it? And did you say that the number was irrational just to mislead people? 1/9 is rational. Can you please publish a solution to the frog questions? I managed to solve one of them.

vishnu c - 6 years, 1 month ago

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@Vishnu C That's 3 questions there in one go! 1) No, you have to ask a moderator to change the answer to a question. Don't know why. 2) That was an accidental error. It has now been changed. 3)I shall try to post a few solutions to the frogs.

A Former Brilliant Member - 6 years, 1 month ago

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@A Former Brilliant Member A level 1 question,but the names were awesome!!

Adarsh Kumar - 6 years, 1 month ago

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@Adarsh Kumar I think minimum level 2, maximum level 3.

A Former Brilliant Member - 6 years, 1 month ago

@Vishnu C 3)You can now see a solution to the first frog question.

A Former Brilliant Member - 6 years, 1 month ago

Have you changed the question as well..? Initially it was 3A³-3 = 0 instead of 3Ax³-3=0

Rohit Sachdeva - 6 years, 1 month ago

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