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When `x^4 - x^3 - kx^2 - 13x + 2`  is divided by x+3, the remainder is the same as...

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oyechalphut | Student, Grade 10 | (Level 1) Honors

Posted February 25, 2013 at 5:28 AM via web

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When `x^4 - x^3 - kx^2 - 13x + 2`

 is divided by x+3, the remainder is the same as when it is divided by x-5. Determine the value of k.

 x^4-x^3-kx^2-13x+2

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oyechalphut | Student, Grade 10 | (Level 1) Honors

Posted February 25, 2013 at 5:29 AM (Answer #1)

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+kx2*****

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durbanville | High School Teacher | (Level 1) Educator Emeritus

Posted February 25, 2013 at 5:49 AM (Answer #2)

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`(x^4 - x^3- kx^2 - 13x + 2)/ (x+3)`  = R

`(x^4 - x^3 - kx^2 - 13x + 2)/(x+5)` =R

This means that when x=-3 (from x-3)AND when x=5 (from x+5) we have the same remainder. Substitute ,thus:

`(-3)^4 -(-3)^3-k(-3)^2-13(-3)+2=(5)^4-(5)^3-k(5)^2-13(5)+2`

They equal each other because R=R

81-(-27)-9k -(-39)+2=625 -125-25k-65+2

Care with the negative symbols:

81+27-9k+39+2= 437-25k

`therefore`   149 - 9k= 437 -25k

`therefore`   -9k+25k = 437-149

`therefore` 16k=288

`therefore`  k=18

 

Sources:

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durbanville | High School Teacher | (Level 1) Educator Emeritus

Posted February 25, 2013 at 5:56 AM (Answer #3)

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The answer if the equation is changed to  `+kx^2` changes to a negative answer. Thus:

81 +27 +9k +39+2 = 625 -125 +25k -65 + 2

`therefore`  k= - 18

 

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pramodpandey | College Teacher | (Level 3) Valedictorian

Posted February 25, 2013 at 11:42 AM (Answer #5)

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`f(x)=x^4-x^3-k x^2-13x+2` 

calculate  f(-3) and f(5)

put  f(-3)=f(5)

i.e.

81+27-9k+39+2=625-125-25k-65+2

147-9k=435-25k

25k-9k=435-147

16k=288

k=18

 

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