Turn on thread page Beta
    • Thread Starter
    Offline

    8
    ReputationRep:
    I have no clue how to do this question! Any help would be appreciated.

    Solve the following equations, giving your answer in the exact form (i.e. involving square roots)

    3x^2 + 8x + 2=0


    Here is my answer, I know this is wrong but I am not sure where I am going wrong.

     x = \frac{-8 \pm \sqrt{40}}{6}

    If someone could give me directions as to where I am going wrong here it would be great.
    Offline

    14
    you use an equation for the quadratic formulae



    where a=3 b=8 and c=2

    put your values in and simplify the b^2 - 4ac bit
    Offline

    1
    ReputationRep:
    This should help.
    Offline

    14
    ReputationRep:
    I don't see what's wrong.
    • PS Helper
    Offline

    14
    ReputationRep:
    PS Helper
    What i find helps alot is to not just plug everything into the caluclutor. Do the (b^2-4ac) first and the 2a then input it into your calculator.
    Offline

    1
    ReputationRep:
    Perhaps try and complete the square.
    3(x^2+(8/3)x+(2/3))
    3(x^2+(8/3)x+(16/9)-(16/9)+(2/3))
    3((x+(4/3))^2)-(10/9)
    3(x+(4/3))=(10/9)^(1/2)
    • Thread Starter
    Offline

    8
    ReputationRep:
    t
    (Original post by Keoje)
    I don't see what's wrong.

    The answer in the book is:

     2x + y = 8

     4x^2 + 3y^2 = 52

     8 - 2x = Y

     4x^2 + 3(8 - 2x)^2 = 52

     4x^2 + 3(64 - 16x - 16x +4x^2) = 52

     4x^2 + 192 - 96x + 12x^2 = 52

     16x^2 - 96x + 140 = 0

     16(x^2 - 6x + \frac {35}{4}) = 0

     (x - 3)^2 + \frac {34}{4} = 0

     (x - 3)^2 -\frac {9}{1} + \frac {34}{4} = 0

     (x - 3)^2 -\frac {36}{4} + \frac {35}{4} = 0

     (x - 3)^2 -\frac {1}{4} = 0



    Don't see how to get to that answer :shifty:
    Offline

    14
    ReputationRep:
    (Original post by Shakaa)
    The answer in the book is:



    Don't see how to get to that answer
    It is the same. Just that is simplified version.

    square root = sqr

    sqr(40) = sqr(4)sqr(10)
    = 2 sqr(10)

    Do you know what to do now?
    • Thread Starter
    Offline

    8
    ReputationRep:
    Ah, I see now. Thanks!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 8, 2010

University open days

  • Sheffield Hallam University
    City Campus Postgraduate
    Wed, 17 Oct '18
  • Northumbria University
    All faculties Undergraduate
    Wed, 17 Oct '18
  • Staffordshire University
    Nursing and Midwifery Undergraduate
    Wed, 17 Oct '18
Poll
Who is most responsible for your success at university
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Equations

Best calculators for A level Maths

Tips on which model to get

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.