1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Poly Factoring

  1. Mar 31, 2009 #1
    1. The problem statement, all variables and given/known data
    determine the interval algebraically for -2(x-1)(2x+5)(x-7)>0



    3. The attempt at a solution
    the zeroes are 1. -2.5, 7

    what do i do with the -2 in front?
     
  2. jcsd
  3. Mar 31, 2009 #2

    Mentallic

    User Avatar
    Homework Helper

    If you graph [tex]y=(x-1)(2x+5)(x-7)[/tex] and then multiply the function by 2, so now you have the graph [tex]y=2(x-1)(2x+5)(x-7)[/tex] and finally, take the negative.

    Now do you know what [tex]y=-2(x-1)(2x+5)(x-7)[/tex] looks like?
     
  4. Mar 31, 2009 #3
    i think ive figured it out, so basically i would divide both sides by -2, and when i divide and an equality by a -, i will hav eot change the direction of the sign
     
  5. Mar 31, 2009 #4

    Mentallic

    User Avatar
    Homework Helper

    Yes you can do that too. But understanding what happens to the function when you multiply it by a negative constant would be a useful tool to have in your arsenal :wink:
     
  6. Apr 1, 2009 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    As you say, the zeroes are -2.5, 1, and 7. Suppose x< -2.5. Then each of the factors is negative. Since there are 4 factors, counting the '-2', there product, and the function value, is positive. Now take x between -2.5 and 1. The single factor (2x+ 5)= -2(x- 2.5) changes sign so there are now three negative factors: the function value is negative between -2.5 and 1. Take x between 1 and 7. Now the x-1 factor changes sign to postive and there are now 2 negative factors: the function value is positive between 1 and 7. Finally, if x> 7, all factors except the '-2' are positive: for x> 7, the function value is negative.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Poly Factoring
  1. Factor This (Replies: 3)

  2. Factorize (Replies: 6)

  3. Factoring a polynomial (Replies: 4)

Loading...