Largest n

Find the largest integer value of n n such that n + 10 n+10 divides n 3 + 100 n^3+100 .


The answer is 890.

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3 solutions

Otto Bretscher
Oct 12, 2015

By long division, n 3 + 100 = ( n 2 10 n + 100 ) ( n + 10 ) 900 n^3+100=(n^2-10n+100)(n+10)-900 so n + 10 n+10 must divide 900...highest n n is n = 890 n=\boxed{890}

Yes , this is the easiest method :)

Nihar Mahajan - 5 years, 8 months ago

Exactly Same Way.

Kushagra Sahni - 5 years, 8 months ago
Kalpok Guha
Oct 12, 2015

( n + 10 ) 3 = n 3 + 1000 + 30 n ( n + 10 ) (n+10)^3=n^3+1000+30n(n+10)

If n 3 + 100 n^3+100 is divisible by n + 10 n+10

Then n + 10 n+10 must divide n 3 + 1000 + 30 n ( n + 10 ) ( n 3 + 100 ) = 30 n ( n + 10 ) + 900 n^3+1000+30n(n+10)-(n^3+100)=30n(n+10)+900

So n + 10 n+10 must divide 900 900

Hence the largest value of n n is 900 10 = 890 900-10=\boxed{890}

Arulx Z
Nov 21, 2015

By polynomial division,

n 3 + 100 n + 10 = n 2 10 n + 100 + 900 n + 10 \frac { { n }^{ 3 }+100 }{ n+10 } ={ n }^{ 2 }-10n+100+\frac { -900 }{ n+10 }

where 900 n + 10 \frac { -900 }{ n+10 } is the remainder. Since we want to find the largest n n , value of denominator must be maximized, while keeping the remainder 0.

Largest number which completely divides -900 is 900 = 900 \left| -900 \right| =900 .

Therefore,

n + 10 = 900 n = 890 n+10=900\\ n=890

Moderator note:

Simple standard approach of solving such divisibility questions.

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