Math

solve the equation 20x^3 +44x^2 -17x -5 given that -5/2 is a zero of f(x) 20x^3 +44x^2 -17x -5

I used synthetic division and got 20x^2-6x-2=0

took 2 and divided it out of that equation

2(x+5/2)=10x^2 -3x-1
then i factored it out the right side of the equation

(x+5/2)=(5x+1)(2x-1)

then i solved for x on each and got

-5/2, -1/5, 1/2

is this correct?

  1. 👍 0
  2. 👎 0
  3. 👁 192
asked by sarah
  1. since x = -5/2 , one of the factors had to be (2x+5)

    when you divide f(x) by 2x+5 you get

    10x^2 - 3x - 1, not 20x^2 - 6x - 2

    I know that when you set your answer of

    20x^2 - 6x - 2 = 0 you get the same as my result when I set it mine to zero.

    You have to be careful when using synthetic division by dividing polynomials by factors of the form ax ± b
    it is safer to use long division for that.

    you then make the statement
    (x+5/2)=(5x+1)(2x-1)

    that is just wrong, they are not "equal"

    what you have to say is
    20x^3 +44x^2 -17x -5 = 0
    (2x+5)(10x^2 - 3x - 1) = 0
    (2x+5)(5x+1)(2x-1) = 0
    then x = -5/2 , we knew that, or
    x = -1/5 or x = 1/2

    I know you had those answers, but with me you would lose marks for bad form in the solution.

    1. 👍 0
    2. 👎 0
    posted by Reiny

Respond to this Question

First Name

Your Response

Similar Questions

  1. math

    Simplify the given equation. 17x - 6 + 3x - 5 = x + 11 + 4x A)20x - 11 = 5x + 11 B)20x + 1 = 5x + 11 C)9x = 16x

    asked by nicky on March 8, 2010
  2. Algebra-Please check

    5 - sqrt of 20x + 4 >= -3 5- 20x + 4 >= -3 5-4 - 20x >= -3 1 - 20x >= -3-1 -20x >= -4 x

    asked by Juliette on October 12, 2010
  3. math

    solving equation 20x-7=2+17x

    asked by kathie on September 29, 2011
  4. math

    Tina has a pet sitting business. She charges a flat service fee of $20, plus $20 per day for each animal. If one of her customers spent less than $100 on one animal, which of the following inequalities could be used to solve for

    asked by abella on December 7, 2018
  5. math

    5(3+4x)-6>=129 I get 2 different answers on this one. 15+20x-6>=129 15+20x-6+6>=129+6 15+20x>=135 15-15+20x>=135-15 20x>=120 20x/20>=120/20 x>=6 Is this worked out properly, are there any shortcuts?

    asked by barb on August 22, 2010
  6. Math

    Find the intersection of two lines. i have the answer just please tell me how it was made 4x-3y-4=0 , 4x+2y+5=0 -5y/-5 = 9/-5 y= 9/5 4x-3(-9/5)-4=0 5(4x+27/5-4=0) 20x+27-20=0 20x+7=0 20x/20=-7/20 x=-7/20 (-7/20, -9/5

    asked by Joy on July 1, 2014
  7. Algebra 1

    Are these right? xy - 3x - 8y + 24 (3x-y)-(8y+24) 8y+24 4x^2 + 20x + 5y +xy 36x+(5y+x) 36x-5y I don't think so it's right.Your question xy-3x-8y+24 is itself the answer.It cannot be further calculated bcause it doesn't have the

    asked by mike on March 8, 2007
  8. Microbiology

    You need 3.5L of 50mM NaCl from your 20X stock. How would you accomplish this: 20X stock __________ml Pure Water ___________ml From whatever number I plugged in trying to solve it, I got: 175ml of 20X stock and 3,430ml of Pure

    asked by John on March 27, 2013
  9. maths

    1a) Solve the each of these equations by factorising the left hand side into a product of linear factors: (i) x^2 - 6x - 40 = 0 (ii) 3x^2 + 20x - 7 = 0 (b) For each question in part (a), check your solutions by substituting them

    asked by Michael on October 24, 2016
  10. maths

    1a) Solve the each of these equations by factorising the left hand side into a product of linear factors: (i) x^2 - 6x - 40 = 0 (ii) 3x^2 + 20x - 7 = 0 (b) For each question in part (a), check your solutions by substituting them

    asked by Saphina AlMatary on October 24, 2016

More Similar Questions