What must be subtracted from the polynomial $f(x)\ =\ x^4\ +\ 2x^3\ -\ 13x^2\ -12x\ +\ 21$ so that the resulting polynomial is exactly divisible by $x^2\ -\ 4x\ +\ 3$?


Given:


Given polynomial is $f(x)\ =\ x^4\ +\ 2x^3\ -\ 13x^2\ -12x\ +\ 21$. The divisor is $x^2\ -\ 4x\ +\ 3$.


To do:


We have to find the polynomial that must be added to the polynomial $f(x)\ =\ x^4\ +\ 2x^3\ -\ 13x^2\ -12x\ +\ 21$ so that the resulting polynomial is exactly divisible by  $x^2\ -\ 4x\ +\ 3$.

Solution:

Let the remainder when $x^2\ -\ 4x\ +\ 3$ divides $f(x)\ =\ x^4\ +\ 2x^3\ -\ 13x^2\ -12x\ +\ 21$ be $r(x)$.

Therefore,

Dividend$=x^4+2x^3-13x^2-12x+21$

Divisor$=x^2-4x+3$

 $x^2-4x+3$)$x^4+2x^3-13x^2-12x+21$($x^2+6x+8$

                       $x^4-4x^3+3x^2$

                      ------------------------------------

                                $6x^3-16x^2-12x+21$

                                 $6x^3-24x^2+18x$            

                               --------------------------

                                              $8x^2-30x+21$

                                             $8x^2-32x+24$

                                          -----------------------

                                                        $2x-3$

Remainder$r(x)=2x-3$

If we subtract the remainder from the dividend then it is completely divisible by the divisor.

The polynomial that must be added to the polynomial $f(x)\ =\ x^4\ +\ 2x^3\ -\ 13x^2\ -12x\ +\ 21$ so that the resulting polynomial is exactly divisible by $x^2\ -\ 4x\ +\ 3$ is $2x-3$.

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Updated on: 10-Oct-2022

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