The remainder is not this!

Algebra Level 3

Let f ( x ) = x 4 + x 3 + x 2 + x + 1 f(x) = x^4 + x^3 + x^2 + x + 1 . Find the remainder when f ( x 5 ) f(x^5) is divided by f ( x ) f(x) .

3. 5. 2. 0. 1.

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.

2 solutions

Hugh Sir
Nov 25, 2018

f ( x ) = x 4 + x 3 + x 2 + x + 1 f(x) = x^{4}+x^{3}+x^{2}+x+1

f ( x 5 ) = x 20 + x 15 + x 10 + x 5 + 1 f(x^{5}) = x^{20}+x^{15}+x^{10}+x^{5}+1

f ( x 5 ) = ( x 20 1 ) + ( x 15 1 ) + ( x 10 1 ) + ( x 5 1 ) + 5 f(x^{5}) = (x^{20}-1)+(x^{15}-1)+(x^{10}-1)+(x^{5}-1)+5

Notice that ( x 20 1 ) (x^{20}-1) is divisible by ( x 5 1 ) (x^{5}-1) .

This is also true for ( x 15 1 ) (x^{15}-1) , ( x 10 1 ) (x^{10}-1) and ( x 5 1 ) (x^{5}-1) .

Also notice that ( x 5 1 ) (x^{5}-1) is divisible by f ( x ) f(x) .

Hence, the remainder when f ( x 5 ) f(x^{5}) is divided by f ( x ) f(x) is 5 5 .

Aaghaz Mahajan
Nov 26, 2018

Another approach is using the Factor Theorem...........see that the root of f(x) = 0 is simply the fifth root of unity and you are done!!!

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...