Cube Roots of Cubes of Cubes

Algebra Level 1

3 3 3 3 = ? \Huge \color{#69047E}\sqrt[3]{\color{#20A900}3^{\color{#3D99F6}{3}^{\color{#D61F06}{3}}}} \color{#EC7300}=\ ?

Hint :

  • 3 3 3 = 3 ( 3 3 ) \displaystyle \large 3^{3^3} = 3^{ \left(3^3 \right) }
  • 3 3 3 ( 3 3 ) 3 \displaystyle \large 3^{3^3} \ne { \left(3^3 \right) }^3
3 3 3^3 3 2 3 3^{2 ^{3}} 3 3 2 3^{3 ^ {2}} ( 3 ) 3 \big(\sqrt{3}\big)^3

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7 solutions

Arul Kolla
Oct 1, 2018

Relevant wiki: Rules of Exponents

x 3 \sqrt[3]{x} can be expressed as x 1 3 x^{\frac{1}{3}} . Thus, the expression becomes ( 3 3 3 ) 1 3 \large \color{#20A900}(3^{\color{#3D99F6}{3}^{\color{#D61F06}{3}}})^{\color{#69047E}\frac{1}{3}} which equals ( 3 27 ) 1 3 \large \color{#20A900}(3^{\color{#EC7300}{27}})^{\color{#69047E}\frac{1}{3}} which equals 3 9 \large \color{#20A900}3^{\color{grey}{9}} or 3 3 2 \large \boxed{\color{#20A900}3^{\color{#3D99F6}{3}^{\color{#D61F06}{2}}}}

Simply Clever

Uttam Manher - 2 years, 8 months ago

Mathematics requires a different brain structure it seems!

Athmanathan Seetharaman - 2 years, 8 months ago

It’s true, I forgot to aplay they exponent rule.

Marco Graf - 2 years, 8 months ago

My algebra is clearly not good enough I see 3 3 3 as 27. Don’t see how the brackets in these sense make a difference. Feeling a bit stupid

Simon Austin - 2 years, 8 months ago

wow, I'm so envy your thinking, that's so simple but easy and useful!!!

Qiao Qiao - 2 years, 8 months ago

I am literally clueless

Tony Hines - 2 years, 8 months ago
Ram Mohith
Oct 7, 2018

3 3 3 3 = 3 3 3 × 3 1 = 3 3 2 \large {\color{#E81990}\sqrt[3]{{\color{#333333}3}^{\color{#3D99F6}3^3}}} = 3^{{\color{#3D99F6}3^3} \times {\color{#E81990}3^{-1}}} = \boxed{\color{#20A900}3^{3^2}}


Note that in general we can write x n \large \color{#E81990} \sqrt[n]{\color{#3D99F6}x} as x 1 n = x n 1 \large {\color{#3D99F6}x}^{\color{#E81990}\frac{1}{n}} = {\color{#3D99F6}x}^{\color{#E81990}n^{-1}}

Thank you but can we take this as a rule ?

Fatim Zahra - 2 years, 8 months ago

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Yeah! However it isn't a rule, it's just another form of x 1 n x^{\frac{1}{n}}

Prem Chebrolu - 2 years, 8 months ago

It's a exopenential law

Hardik 3004 - 2 years, 8 months ago

Very elegant.

rawrina wehbe - 2 years, 8 months ago

👏🏾 well done

Fezzoh Mboyz - 2 years, 8 months ago

Based on the general rule, the base will be raised to the 1/3 power or 3 to the negative 1 power. And the base is all (3 to the 3 power to the 3 power). All this will be raised to the 1/3 power. Or not?

Juliana Hida - 2 years, 7 months ago
Venkatachalam J
Oct 7, 2018

Relevant wiki: Rules of Exponents

Nice display. How did you do that ?

Jesse Otis - 2 years, 8 months ago

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Used MS-office.

Venkatachalam J - 2 years, 8 months ago

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Is it MS Word.

Ram Mohith - 2 years, 8 months ago

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@Ram Mohith Yes, used MS word.

Venkatachalam J - 2 years, 8 months ago

Hey, I love your picture! How can you do that?

Qiao Qiao - 2 years, 8 months ago

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Thank you. Used Used MS-office.

Venkatachalam J - 2 years, 8 months ago
Blan Morrison
Oct 1, 2018

Relevant wiki: Rules of Exponents

3 3 3 3 = 3 ( 3 3 1 3 ) = 3 3 3 3 1 \sqrt[3]{3^{3^{3}}}=3^{\left(3^3 \cdot \frac{1}{3}\right)}=3^{3^3\cdot 3^{-1}} 3 3 3 3 1 = 3 3 3 1 = 3 3 2 3^{3^3\cdot 3^{-1}}=3^{3^{3-1}}=\boxed{3^{3^{2}}}

(3^27)^(1/3)=3^9

Chukwuka Odigbo
Oct 14, 2018

We're simple looking for the cube root of 3 raised to the power 27.

That's 3^9, ie 3 raised to 3 squared.

Nick Pretzel
Oct 14, 2018

Note that:

  1. x n × x m = x n + m x^n × x^m = x^{n+m}
  2. ( x n ) m = x n × m (x^n)^m = x^{n×m}
  3. x n m = x ( n m ) x^{n^m} = x^{(n^m)}
  4. x n = x 1 n \sqrt[n]{x} = x^{\frac 1n}

So we have 3 3 3 3 \sqrt[3]{3^{3^3}} which can be rewritten (using rules 3 & 4 above. 1 was only included to give an idea of how exponents work. Note how rule 1 turns multiplication into addition and is the basis for logarithms) ( 3 27 ) 1 3 (3^{27})^{\frac 13} and using rule 2 that gives us 3 9 = 3 3 2 3^9 = 3^{3^2}

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