Algebra Question #10

Algebra Level 4

What is the remainder when ( 8 101 + 4 101 + 2 101 + 1 ) (8^{101} + 4^{101} + 2^{101} + 1) is divided by ( 2 100 1 ) ? (2^{100} - 1 )?


The answer is 15.

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3 solutions

Kunal Verma
Feb 21, 2015

S o y e s t h i s i s n o t a N u m b e r T h e o r y q u e s t i o n . W e l e t x = 2 100 O u r d i v i s o r = g ( x ) = x 1 N o w t h e p o l y n o m i a l t o d i v i d e : p ( x ) = 8 101 + 4 101 + 2 101 + 1 = 8. 8 100 + 4. 4 100 + 2. 2 100 + 1 = 8 x 3 + 4 x 2 + 2 x + 1 U s i n g R e m a i n d e r t h e o r e m , w e p u t x = 1 p ( 1 ) = 8. 1 3 + 4. 1 2 + 2.1 + 1 = 8 + 4 + 2 + 1 = 15 So\quad yes\quad this\quad is\quad not\quad a\quad Number\quad Theory\quad question.\\ \\ We\quad let\quad x\quad =\quad { 2 }^{ 100 }\\ \\ Our\quad divisor\quad =\quad g(x)\quad =\quad x\quad -\quad 1\\ \\ Now\quad the\quad polynomial\quad to\quad divide:-\\ \\ p(x)\quad =\quad { 8 }^{ 101 }\quad +\quad { 4 }^{ 101 }\quad +\quad { 2 }^{ 101 }\quad +\quad 1\\ \quad \quad \quad \quad =\quad 8.{ 8 }^{ 100 }\quad +\quad 4.{ 4 }^{ 100 }\quad +\quad 2.{ 2 }^{ 100 }\quad +\quad 1\\ \quad \quad \quad \quad =\quad 8{ x }^{ 3 }\quad +\quad 4{ x }^{ 2 }\quad +\quad 2x\quad +\quad 1\\ \\ Using\quad Remainder\quad theorem,\quad we\quad put\quad x\quad =\quad 1\\ \\ \therefore \quad p(1)\quad =\quad 8.{ 1 }^{ 3 }\quad +\quad 4.{ 1 }^{ 2 }\quad +\quad 2.1\quad +\quad 1\\ \quad \quad \quad \quad \quad \quad \quad =\quad 8\quad +\quad 4\quad +\quad 2\quad +\quad 1\\ \quad \quad \quad \quad \quad \quad \quad =\quad \boxed { 15 } \\

Excellent :D

Paul Ryan Longhas - 6 years, 3 months ago

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Thanks. c:

Kunal Verma - 6 years, 3 months ago

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Not bad Kunal.

Aayush Patni - 6 years, 3 months ago

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@Aayush Patni Short and simple

Aayush Patni - 6 years, 3 months ago

Oh my god! How on Earth did you spot this? Excellent work! :D

Mehul Arora - 5 years, 11 months ago

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Thanks. c:

Kunal Verma - 5 years, 11 months ago

Excellent .

Sai Ram - 5 years, 10 months ago

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Thank you. c:

Kunal Verma - 5 years, 10 months ago

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Brilliant solution

Sai Ram - 5 years, 10 months ago

brilliant!!!!!!!

bhumika sharma - 5 years, 9 months ago

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Thanks. :')

Kunal Verma - 5 years, 9 months ago

amazing solution!

Swastik Sahoo - 5 years, 4 months ago

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Thanks. c:

Kunal Verma - 5 years, 4 months ago
Paul Ryan Longhas
Nov 25, 2014

(8^{101} + 4^{101} + 2^{101} + 1) / 2^{100} - 1 =( 8(8^100) + 4(4^100) + 2(2^100) + 1)/2^{100} - 1. Let x = 2^100, so ----> (8x^3 + 4x^2 + 2x + 1)/ x - 1. By Remainder Theorem ---> 8(1)^3 + 4(1)^2 + 2(1) +1 = 15 answer

a=2^100, A=a-1, B=8a^3+4a^2+2a+1; B/A do the division, reminder would be 15.

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