How many 17s?

17 2 + 17 2 + 17 2 + . . . + 17 2 + 17 2 + 17 2 = 17 2 + 17 2 + 17 2 \sqrt { { 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 }+...+{ 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 } }\\ ={ 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 }

How many times should 17 2 {17}^{2} appear under the square root sign for the equation above to be true?


The answer is 2601.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

27 solutions

1 7 2 + 1 7 2 + 1 7 2 = 3 1 7 2 = 9 1 7 2 1 7 2 = 9 1 7 2 1 7 2 . 9 1 7 2 = 2601 17^2 +17^2+17^2 = 3*17^2 = \sqrt{9*17^2*17^2} =\sqrt{ \color{#D61F06}{9*17^ 2} *17^2}.\\9*17^2 =\boxed{ 2601 }

superb....!

nidita karkare - 5 years, 1 month ago

Log in to reply

Great ! Simple and obvious !

Abdenour Sahel - 4 years, 11 months ago

How can the answer be 2061 when it is asking for the number of times!!!!!!!!!!!!!

Sandeep Sahoo - 4 years, 11 months ago

Log in to reply

2601 no. of times 17^2 would be under the root.

erica phillips - 3 years ago

I agree, sqrt a square and they cancel each other out. This solution suggests 2601 * 17 which does not equal 17^2 * 3... The answer should be 51!

Blake Payne - 2 years, 8 months ago

what a fantastic explanation man!

Shubh Gulati - 5 years, 6 months ago

wow,,,get outta here man

Mhlely Tre-flip Nkambule - 5 years, 4 months ago

In response to niranjan khanderia....... The answer should be 867 becoz 3 17^2= 867......and (9 17^2 17^2)^1/2 when you take 9 out, how it can be still 9? It should be 3 when it comes out. So 3 17^2= 867 LHS=RHS

prateek gupta - 4 years, 11 months ago

3*17^2=867 wtf get your math together.

Iraklis Pazios - 4 years, 9 months ago

Log in to reply

dude you get your math together it's 9*17^2

Laura Gao - 2 years, 5 months ago

beautiful <3

Atosi Roy - 4 years, 6 months ago

N17'2 = 17'2 + 17'2+ 17'2 there fore 17n =17'2+17'2+17'2 n = 17 + 17 +17 N = 51'2 = (2601)

We can write the equation as follows:

Because appears times under the square root sign, we can write:

Squaring both sides:

Dividing by :

Samuel Cavanagh - 4 years, 5 months ago

Log in to reply

N17'2 = 17'2 + 17'2+ 17'2 there fore 17n =17'2+17'2+17'2 n = 17 + 17 +17 N = 51'2 = (2601)

We can write the equation as follows:

Because appears times under the square root sign, we can write:

Squaring both sides:

Dividing by :

Samuel Cavanagh - 3 years, 4 months ago

did the same way

vansh gupta - 4 years, 4 months ago

amazingly solve this problem.

manish agrawal - 2 years, 8 months ago

i wasn't expecting that O_O

Graidvel Gomar Gama - 1 year ago

Beautiful explanation. Just great.

Kun Yi Ong - 6 years, 2 months ago

Log in to reply

really grt

Sarthak Singh - 5 years, 6 months ago

3×17×17 is not equal to 9×17×17

Haowei Jiang - 5 years, 3 months ago

Log in to reply

3 = 9 , 3=\sqrt9, so when this three goes inside the square root sign it becomes 9.

Niranjan Khanderia - 5 years, 3 months ago

We can write the equation as follows:

17 2 + 17 2 + 17 2 + . . . + 17 2 + 17 2 + 17 2 = 17 2 + 17 2 + 17 2 \sqrt { { 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 }+...+{ 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 } } ={ 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 }

17 2 + 17 2 + 17 2 + . . . + 17 2 + 17 2 + 17 2 = 17 ( 17 3 ) \sqrt { { 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 }+...+{ 17 }^{ 2 }+{ 17 }^{ 2 }+{ 17 }^{ 2 } } ={ 17 }\left( 17\cdot 3 \right)

Because 17 2 {17}^{2} appears n n times under the square root sign, we can write:

n 17 2 = 17 ( 17 3 ) \sqrt { n\cdot { 17 }^{ 2 } } ={ 17 }\left( 17\cdot 3 \right)

Squaring both sides:

n 17 2 = 17 2 ( 17 2 9 ) n\cdot { 17 }^{ 2 }={ { 17 }^{ 2 } }\left( { 17 }^{ 2 }\cdot 9 \right)

Dividing by 17 2 {17}^{2} :

n = ( 17 2 9 ) n=\left( { 17 }^{ 2 }\cdot 9 \right)

n = ( 289 9 ) n=\left( 289\cdot 9 \right)

n = 2601 \boxed{n=2601}

My immediate answer was 9 LOL. I thought that the 17's were not relevant.

Calvin Lin Staff - 6 years, 5 months ago

Log in to reply

Same here :p

Krishna Sharma - 6 years, 5 months ago

Me too... Hahahahaha

Ajay Aditya - 5 years, 4 months ago

Calvin Lin (staff) please check whether the answers are relevant as I came to this page for an entirely different sum. My email for further info: akhashrajaraam @gmail.com

Akhash Raja Raam - 5 years, 4 months ago

Is it coincidence that I did the same?

Agnishom Chattopadhyay - 6 years, 4 months ago

Log in to reply

Hey even I put 9 first :)

karthik suresh - 5 years, 11 months ago

is that someone answer 51....

Igde Daffananda - 5 years, 9 months ago

Log in to reply

I answered 51 also lol

Bikram Chohan - 5 years, 8 months ago

I answered 51, because 51(17^2) under square root = 867 wich is = (17^2 +17^2 +17^2), I don't know my mistake

Luis Pedro - 5 years, 6 months ago

Log in to reply

@Luis Pedro I did the same thing. because all those (17^2) under a square root cancel to be just 17. 3(17^2)= 867 867/17=51. That's correct maths for sure.

Ryan Hancock - 5 years, 5 months ago

Log in to reply

@Ryan Hancock @Ryan Hancock you have to consider that the sqrt(17²×n) ≠ 17n, but to 17sqrt(n) so that all those 17² don't just cancel to be just 17 each, but the number of 17s also reduces to the square root of the original number of 17²s under the sqrt, so that sqrt(51×17²) = 17 × sqrt(51) = 17 × sqrt(17)× sqrt(3) that's why there aren't just 51 17²s under the sqrt, but 51² (2601) of them such that under the same procedure sqrt(51²×17²) = 51×17 = 3×17×17 = 3×17². I hope it's clear why the answer is 2601

Javier Álvarez - 3 years, 4 months ago

@Luis Pedro 1 7 2 51 < 17 8 = 136 < 867 = 1 7 2 3 \sqrt{17^{2} \cdot 51} < 17 \cdot 8 = 136 < 867 = 17^{2} \cdot 3

Antonio Martínez - 5 years, 1 month ago

i too answered as 9

SARAN .P.S - 5 years, 7 months ago

Victor, very good problem and fun. Thank you for problem.

Heder Oliveira Dias - 6 years, 5 months ago

Great great !how didn't think au bout this !

Abdenour Sahel - 4 years, 11 months ago

The question is not what is the number under the square root sign, but but how many times is the number 17 squared to appear under the square root sign. The number is two, which, when multiplied by nine give the result.

Asher Levitsky - 3 years, 12 months ago
Anweshan Bor
Jan 11, 2015

We can write the equation as

n 1 7 2 = 1 7 2 + 1 7 2 + 1 7 2 \sqrt{n17^{2}} = 17^{2} + 17^{2} + 17^{2}

therefore

17 n = 1 7 2 + 1 7 2 + 1 7 2 n = 17 + 17 + 17 17\sqrt{n} = 17^{2} + 17^{2} + 17^{2} \sqrt{n} = 17 +17+ 17

n = 5 1 2 = 2601 n= 51^{2}=2601

Same solution I used, and definitely the easiest.

Brian Crouch - 4 years, 8 months ago

Easy solution and I have also solved the problem in this method.

Shahriar Rizvi - 4 years, 3 months ago

Easiest method to arrive at the answer

Bhargav Dixit - 5 years, 12 months ago
Leandro Silva
Jul 22, 2015

n × 1 7 2 = 3 × 1 7 2 \sqrt{n\times17^{2}} =3\times 17^{2}

n × 1 7 2 = 9 × 1 7 4 n \times 17^{2} = 9 \times 17^{4}

n = 9 × 1 7 2 = 2601 n = 9\times 17 ^{2} = 2601

The cleanest.

Matteo Vassallo - 4 years, 10 months ago
Aswin T.S.
Feb 3, 2016

Wrong solution mate

James D - 4 years, 8 months ago
William Isoroku
Jan 12, 2015

Rewriting the equation as x = 3 ( 1 7 2 ) \sqrt{x}=3(17^2)

Squaring both sides gives us x = ( 3 ( 1 7 2 ) ) 2 = 1 7 2 ( 1 7 2 ( 9 ) ) x=(3(17^2))^2=17^2(17^2(9)) So 9 ( 1 7 2 ) = 2601 9(17^2)=\boxed{2601}

Romain Milon
Jun 27, 2016

Let S = 1 7 2 + 1 7 2 + . . . + 1 7 2 = k × 1 7 2 S = \sqrt{17^2+17^2+...+17^2} = \sqrt{k \times 17^2} . We know that S = 1 7 2 + 1 7 2 + 1 7 2 = 3 × 1 7 2 S = 17^2+17^2+17^2 = 3 \times 17^2 . From this, we get S 2 = k × 1 7 2 = ( 3 × 1 7 2 ) 2 = 9 × 1 7 4 S^2 = k \times 17^2 = (3 \times 17^2)^2 = 9 \times 17^4 . Let's find k : k = 9 × 1 7 4 1 7 2 = 2601 k = \frac{9 \times 17^4}{17^2} = \boxed{2601} . So 17^2 needs to be 2601 times under the sqare root to let S equals 3 × 1 7 2 3 \times 17^2 .

Thanks for sharing your approach, Romain. The solution is well-presented and is easy to understand.

Pranshu Gaba - 4 years, 11 months ago
Andreas Hansen
Jun 25, 2016

If we let x equal 17,

x = 17 x = 17

we can write the equation like x 2 + x 2 + x 2 = 3 x 2 = x 2 + x 2 + x 2 + + x 2 = n x 2 x^2 + x^2 +x^2 = 3 \cdot x^2 = \sqrt{x^2 + x^2 + x^2 + \ldots + x^2} = \sqrt{n \cdot x^2} Or just

3 x 2 = n x 2 3 \cdot x^2 = \sqrt{n \cdot x^2}

We can now square both sides 9 x 4 = n x 2 9 \cdot x^4 = n \cdot x^2

and isolate n

n = 9 x 4 x 2 = 9 x 2 n = \frac {9 \cdot x^4}{x^2} = 9 \cdot x^2

Now we replace our x with 17 n = 9 1 7 2 = 9 289 = 2601 n = 9 \cdot 17^2 = 9 \cdot 289 = 2601

( 1 7 2 3 ) 2 (17^2 * 3)^2 = 751689

751689 289 \frac{751689}{289} = 2601

This is equal with √(16+16+16+⋯+16+16+16)=16+16+16. There fore to get 48 or 16+16+16 we should have 48*48 in the radical sign. That is 2304. This implies we should have {(2304)/(16)}th 16 in the radical sign. that is 144 16s should have.

Ikram Ibrahim
Sep 5, 2015

n 1 7 2 = 9 × 1 7 4 n = 9 × 1 7 2 = 2601 n 17^2 =9 \times 17^4\\ n= 9\times 17^2=2601

Curtis Clement
Jan 12, 2015

squaring both sides gives 1 7 2 17^{2} + 1 7 2 17^{2} +...+ 1 7 2 17^{2} = 3 2 3^{2} × \times 1 7 4 17^{4} = (9 × \times 1 7 2 17^{2} ) × \times 1 7 2 17^{2} . The term in the brackets tells us how many 1 7 2 17^{2} are required. Let this value be n {n} .

\therefore n {n} = 9 × \times 1 7 2 17^{2} = 2601 \boxed{2601}

Note that: 3 × 1 7 2 = 867 3 \times 17^2 = 867

Then 86 7 2 = 751689 867^2 = 751689 giving us the result: 751689 / 1 7 2 = 2601 751689 / 17^2 = 2601

John Park
Oct 9, 2019

|17^2=x| sqrt(x+x+x+x+x....)=sqrt(ax)| a = number of times x is added| sqrt(ax)=3x| ax=9x^2| a=9x| a=(9)17^2| a=(9)289| a=2601| 17^2 should appear 2601 times under the sqrt.|

William Allen
Feb 11, 2019

We need something who’s square root is 1 7 2 + 1 7 2 + 1 7 2 17^2+17^2+17^2 so let’s look at ( 3 × 1 7 2 ) 2 \sqrt{(3\times 17^{2})^{2}} or 3 2 × 1 7 4 \sqrt{3^{2}\times 17^{4}} , and 1 7 4 = ( 1 7 2 ) 2 = 1 7 2 × 1 7 2 17^{4} = (17^{2})^{2} = 17^{2}\times 17^{2} so we need 1 7 2 17^{2} lots of 1 7 2 17^{2} added together to make a single 1 7 4 17^{4} and we need 3 2 × 1 7 4 3^{2}\times 17^{4} to be rooted. Or 3 2 × 1 7 2 × 1 7 2 \sqrt{3^{2}\times 17^{2}\times 17^{2}} so there needs to be 3 2 × 1 7 2 = 2601 3^{2}\times 17^{2} = \boxed{2601} 1 7 2 17^{2} s added together.

Sswag SSwagf
Sep 23, 2016

simple solution, we can interpret as:

x 1 7 2 = 867 \sqrt{x17^{2}} = 867

17 x = 867 17\sqrt{x} = 867

x = 867 17 \sqrt{x} = \frac{867}{17}

x = 51 \sqrt{x} = 51

x = 2601 x = 2601

Mafia maNiAc
Sep 11, 2016

RHS we have 17^{2}+17^{2}+17^{2}=867 Further it is equal to \sqrt{867×867} On factorising we get- \sqrt{17^{2}×3×867} \sqrt{17^{2}×2601}

Hence,17^{2} should have to appear \boxed{2601} times ... Q.E.D.

Let X = 1 7 2 X=17^{2} . The equation in the question can be rewritten as follows:

n X = 3 X \sqrt{nX}=3X

where n n is the number of X's required under the square root. Solving for n n :

n = 9 X = 9 × 1 7 2 = 2601 n=9X=9\times17^{2}=2601

as required.

Johannes Moerland
Jul 18, 2016

We can rewrite 1 7 2 + . . . + 1 7 2 = 1 7 2 + 1 7 2 + 1 7 2 \sqrt{17^2 + ... + 17^2} = 17^2 + 17^2 + 17^2 as a 1 7 2 = 3 1 7 2 \sqrt{a * 17^2} = 3 * 17^2 . By squaring both sides of the equation, we obtain a 1 7 2 = 9 1 7 4 = a 1 7 2 1 7 2 a = 1 7 2 9 = 2601 a * 17^2 = 9 * 17^4 = a * 17^2 * 17^2 \rightarrow a = 17^2 * 9 = \boxed{2601}

Sayan Das
Jun 21, 2016

We can write the equation as √n.17^2=3.17^2 √k.17^2=3.17^2;where n=k.17^2 K=9 n=9×17^2=2601

Raun Kerstan
Mar 3, 2016

17^2 * 9 = 2601

David Giblin
Feb 29, 2016

Rewrite all the 17s as a 1 7 2 \sqrt{a17^{2}} and equate this to 3 ( 1 7 2 ) 3(17^{2}) Square both sides... a . 1 7 2 = ( 3.1 7 2 ) 2 = 9.1 7 2 a.17^{2} = (3.17^{2})^{2} = 9.17^{^{2}} The number of 17s required is a which is a = 9.1 7 2 = 2601 a = 9.17^{2}= 2601

Mostakim Shakil
Dec 14, 2015

we can solve this in this way --- ( 3 * 17^2)^2=(9 * 17^2 * 17^2)=2601 * 17^2 , as we need to keep 3...... squared 17.

Let x be number of times 17^2 will appear
therefore, (x.17^2)^1/2 = 3.17^2
squaring both sides,
x.17^2 = 9.17^2.17^2
x.17^2 = 2601.17^2
x = 2601




Keshav Bassi
Aug 2, 2015

We can derive algebraic formula for this. By deriving the formula i.e. 9×a^2 and putting a=17 we get 9×17^2 =9*289=2601

Vineet Singh
Jul 16, 2015

We need LHS to be 9 17^4 and that can happen if there are 9 17^2 = 2601 terms inside the square root.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...