Comparing coefficients C1! Bleugh!

Maths and statistics discussion, revision, exam and homework help.

Announcements Posted on
TSR launches Learn Together! - Our new subscription to help improve your learning 16-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
Sign in to Reply
  1. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Comparing coefficients C1! Bleugh!
    OCR Jan 11 Question 2!

    Find constants P and Q

    (x-p)(2x^2 + 9x +10) = (x^2-4)(2x + q)
    I expanded both sides and got
    2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q

    Now, when i look at that.. I honestly do not know what to do next :/
    I can compare coefficients with simple equations, but this one is bleugh :/

    Can someone guide me?
  2. Blazy's Avatar
    • Exalted Member
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    OCR Jan 11 Question 2!

    Find constants P and Q

    (x-p)(2x^2 + 9x +10) = (x^2-4)(2x + q)
    I expanded both sides and got
    2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q

    Now, when i look at that.. I honestly do not know what to do next :/
    I can compare coefficients with simple equations, but this one is bleugh :/

    Can someone guide me?
     2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q

    At the moment, it doesn't look too helpful to have a mixture of numbers, p's and q's, so put all the x's with a integer coefficient on one side and the p's + q's onto another, then compare.
  3. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    OCR Jan 11 Question 2!

    Find constants P and Q

    (x-p)(2x^2 + 9x +10) = (x^2-4)(2x + q)
    I expanded both sides and got
    2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q

    Now, when i look at that.. I honestly do not know what to do next :/
    I can compare coefficients with simple equations, but this one is bleugh :/

    Can someone guide me?
      2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q \\ 2x^3 + (9-2p)x^2 + (10-9p)x -10p = 2x^3 + qx^2 -8x -4q

    Now compare the coefficients,
     9-2p=q \\ 10-9p=-8

    Solve the equations to find the values of 'p' and 'q'.
  4. Brit_Miller's Avatar
    • Benevolent Member
    • Location: Bristol
    • Posts: 683
    Re: Comparing coefficients C1! Bleugh!
    Numbers on one side, variables on the other, then you can work them out easily.

    9x^2 = 2px^2 + qx^2
    18x = 9px
    10p - 4q = 0x
    Last edited by Brit_Miller; 12-05-2012 at 00:08.
  5. WarriorInAWig's Avatar
    • Adored and Respected Member
    • Location: Wigan
    • Posts: 407
    Re: Comparing coefficients C1! Bleugh!
    You need to gather your coefficients together. By this I mean simplify the left and right hand sides WITHOUT bringing anything on one side to the other.

    Next, look at the coefficients for x^3, x^2, x and the constant term and create 4 equations of the form:

    Left Hand side Right
    x^3: ??? = ???
    x^2: ??? = ???
    x: ??? = ???
    constant: ??? = ???

    Fill in the blanks and solve each equation and you should get your p and q values.
  6. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by raheem94)
      2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q \\ 2x^3 + (9-2p)x^2 + (10-9p)x -10p = 2x^3 + qx^2 -8x -4q

    Now compare the coefficients,
     9-2p=q \\ 10-9p=-8

    Solve the equations to find the values of 'p' and 'q'.
    Hey, do you self teach yourself?
  7. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    Hey, do you self teach yourself?
    Yes
  8. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by WarriorInAWig)
    You need to gather your coefficients together. By this I mean simplify the left and right hand sides WITHOUT bringing anything on one side to the other.

    Next, look at the coefficients for x^3, x^2, x and the constant term and create 4 equations of the form:

    Left Hand side Right
    x^3: ??? = ???
    x^2: ??? = ???
    x: ??? = ???
    constant: ??? = ???

    Fill in the blanks and solve each equation and you should get your p and q values.
    Thanks for the tips!
  9. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    May i ask.. How? what resources do you use
  10. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by Brit_Miller)
    Numbers on one side, variables on the other, then you can work them out easily.

    9x^2 = 2px^2 + qx^2
    18x = 9px
    10p - 4q = 0x
    Thanks for the tips!
  11. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by Blazy)
     2x^3 + 9x^2 + 10x - 2px^2 - 9px -10p = 2x^3 + qx^2 - 8x - 4q

    At the moment, it doesn't look too helpful to have a mixture of numbers, p's and q's, so put all the x's with a integer coefficient on one side and the p's + q's onto another, then compare.
    Thanks!!
  12. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    May i ask.. How? what resources do you use
    I just use the edexcel modular text books to learn maths.
  13. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by raheem94)
    I just use the edexcel modular text books to learn maths.
    Hmm, i'm on OCR. So you use the textbooks? Dayum, they're so black and white and dull :/ lol

    I think i should start using them!

    I usually learn everything on mymaths then just papers

    Then again, i do end up with Cs :P
  14. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    Hmm, i'm on OCR. So you use the textbooks? Dayum, they're so black and white and dull :/ lol

    I think i should start using them!

    I usually learn everything on mymaths then just papers

    Then again, i do end up with Cs :P
    Edexcel ones aren't black and white, if you want to have a look at them, then you can download them, do you need the link?
  15. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by raheem94)
    Edexcel ones aren't black and white, if you want to have a look at them, then you can download them, do you need the link?
    It's okay lol

    I can't change boards :P School won't allow it
  16. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    It's okay lol

    I can't change boards :P School won't allow it
    But you can use the books for explanation.
  17. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
    (Original post by raheem94)
    But you can use the books for explanation.
    oo, okay then

    I shall have the link
  18. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
  19. jameslad's Avatar
    • Exalted Member
    • Posts: 307
    Re: Comparing coefficients C1! Bleugh!
  20. raheem94's Avatar
    • TSR Demigod
    • Posts: 5,512
    Re: Comparing coefficients C1! Bleugh!
    (Original post by jameslad)
    Amazing!

    Yo should set up a youtube channel and post videos about maths!
    There are many better mathematicians to do this.

    Remember the solution bank of these books only works in internet explorer and mozilla firefox.

    Running it on firefox may require some changing in firefox setting.

    It runs in internet explorer, but if you are using internet explorer 9 then you will need to watch my video to learn how to run it.
Sign in to Reply
Share this discussion:  
Article updates
Moderators

We have a brilliant team of more than 60 volunteers looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.