Math is radical!

Algebra Level 3

Consider the following equation 1 + 2 + 2 ( 2 + 2 ) = a + b + c d e + f 1+\sqrt{2}+\sqrt{2\left(2+\sqrt{2}\right)}=\sqrt{\frac{a+\sqrt{b+\sqrt{c}}}{d-\sqrt{e+\sqrt{f}}}} where a , b , c , d , e , f \large\color{#3D99F6}{a,b,c,d,e,f} are integers. Calculate a × b × c × d × e × f \large\color{#3D99F6}{a\times b\times c\times d\times e\times f} .


The answer is 64.

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1 solution

Michael Mendrin
Aug 21, 2014

First, note that

( 1 + 2 + 2 ( 2 + 2 ) ) 2 = { \left( 1+\sqrt { 2 } +\sqrt { 2(2+\sqrt { 2 } ) } \right) }^{ 2 }=

7 + 4 2 + 4 2 + 2 + 2 2 ( 2 + 2 ) 7+4\sqrt { 2 } +4\sqrt { 2+\sqrt { 2 } } +2\sqrt { 2(2+\sqrt { 2 } ) }

The right side is then

7 + 4 2 + 4 2 + 2 + 2 2 ( 2 + 2 ) 1 = \sqrt { \dfrac { 7+4\sqrt { 2 } +4\sqrt { 2+\sqrt { 2 } } +2\sqrt { 2(2+\sqrt { 2 } ) } }{ 1 } }=

( 6 + 2 + 4 2 + 2 ) ( 2 + 2 ) ( 2 2 ) ( 2 + 2 ) = \sqrt { \dfrac { (6+\sqrt { 2 } +4\sqrt { 2+\sqrt { 2 } } )(2+\sqrt { 2 } ) }{ (2-\sqrt { 2 } )(2+\sqrt { 2 } ) } } =

( 6 + 2 + 4 2 + 2 ) ( 2 2 ) = \sqrt { \dfrac { (6+\sqrt { 2 } +4\sqrt { 2+\sqrt { 2 } } ) }{ (2-\sqrt { 2 } ) } } =

( 2 + 2 + 2 ) ( 2 + 2 + 2 ) ( 2 2 + 2 ) ( 2 + 2 + 2 ) = \sqrt { \dfrac { (2+\sqrt { 2+\sqrt { 2 } } )(2+\sqrt { 2+\sqrt { 2 } } ) }{ (2-\sqrt { 2+\sqrt { 2 } } )(2+\sqrt { 2+\sqrt { 2 } } ) } } =

2 + 2 + 2 2 2 + 2 \sqrt { \dfrac { 2+\sqrt { 2+\sqrt { 2 } } }{ 2-\sqrt { 2+\sqrt { 2 } } } }

And so

a = b = c = d = e = f = 2 a=b=c=d=e=f=2

and the answer is 64 64 .

Is there a specific identity for that, ( 2 2 ) = ( 2 2 + 2 ) ( 2 + 2 + 2 ) (2-\sqrt2)=(2-\sqrt{2+\sqrt2})(2+\sqrt{2+\sqrt2}) . Such as a a = a-\sqrt{a}=

Trevor Arashiro - 6 years, 9 months ago

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Oh, nothing remarkable or unique or beautiful. For example, if b = a ( a 1 ) b=a(a-1) and c = a c=a , then you'll get a a a-\sqrt { a }

Michael Mendrin - 6 years, 9 months ago

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Please explain how.

Niranjan Khanderia - 6 years, 9 months ago

For example ....,then you'll get ?????

Niranjan Khanderia - 6 years, 9 months ago

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@Niranjan Khanderia Example:

( 11 + 110 + 11 ) ( 11 110 + 11 = (11+\sqrt { 110+\sqrt { 11 } } )(11-\sqrt { 110+\sqrt { 11 } } =

11 11 11-\sqrt { 11 }

An unremarkable example, except that this is true in both decimal and binary. Just a quirk example.

Michael Mendrin - 6 years, 9 months ago

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@Michael Mendrin Thank you.

Niranjan Khanderia - 6 years, 9 months ago

this problem has more than one answer !!!! Check a=17 , b=208 , c =6272 , d=7 and if √(e+ √f)=32 ( you can put e=0, f=32 or e=27 , f=25 or f=1 , e=31 and ....) it will satisfy the equation. yet the answer is not 64 . the number of solutions are not infinite but it has more than one solution. inform me if i am wrong pls ????

Amirhousein Yousefli - 6 years, 9 months ago

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Amirhousein Yousefi, you are absolutely right. There are more than one possible answer to this problem, and a=17, b=208, c=6772, d=7, e=27, f=25 is one of them, and the product is decidedly not 64. I'd like to reword this problem, but I'm not the problem creator.

Michael Mendrin - 6 years, 9 months ago

Speechless.

A Former Brilliant Member - 6 years, 8 months ago

a = 7 , b = 32, c=0, d= 3, e= 1, f=1 seems to work. Hence the product abdcef = 0

sh mi - 6 years, 9 months ago

a = 7 , b = 32, c=0, d= 3, e= 4, f=0 seems to work. Hence the product abdcef = 0

sh mi - 6 years, 9 months ago

Can you please explain how you get step four from step three !! How to find square root of three terms under square root sign?

Niranjan Khanderia - 6 years, 9 months ago

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It's much easier to see how this works if you worked from the bottom up, i.e., start at the last line, and then start multiplying things out. Factoring radicals is always a tricky process. There are techniques but no simple standard procedure.

Michael Mendrin - 6 years, 9 months ago

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Thank you.

Niranjan Khanderia - 6 years, 9 months ago

The author has corrected the typo. So comment removed.

Niranjan Khanderia - 6 years, 9 months ago

Same method!

Vraj Mistry - 5 years, 11 months ago

@Michael Mendrin please explain me the steps from the 1 in the denominator to 2-2^1/2

Asad Jawaid - 4 years, 4 months ago

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It would have been easier to follow had I put down

2 ( 7 + 4 2 + 4 2 + 2 + 2 2 ( 2 + 2 ) ) 2 = \sqrt { \dfrac {2( 7+4\sqrt { 2 } +4\sqrt { 2+\sqrt { 2 } } +2\sqrt { 2(2+\sqrt { 2 } ) } ) }{ 2 } }=

Michael Mendrin - 4 years, 4 months ago

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OH MY NOW I GET IT,THANKS PAL. :D

Asad Jawaid - 4 years, 4 months ago

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