Turn on thread page Beta
    • Thread Starter
    Offline

    14
    ReputationRep:
    hey guys I have a question

    if I have 3x^2 -10x +7 = 0

    how do I make x the subject and hence find x ?

    first I made it : 3x^2 -10x = -7

    but I don't know how to rearrange this algebraically
    Offline

    17
    ReputationRep:
    (Original post by kingkongjaffa)
    hey guys I have a question

    if I have 3x^2 -10x +7 = 0

    how do I make x the subject and hence find x ?

    first I made it : 3x^2 -10x = -7

    but I don't know how to rearrange this algebraically
    Quadratic formula or complete the square? (I suggest the former)

    Are you aware of those techniques?
    Offline

    0
    ReputationRep:
    Basically, simply all that you can in the first step.

    3x*2 - 10x +7 = 0 will become
    6x -10x +7 = 0, which will become
    -4x + 7 = 0, which will become
    -4x = -7, so
    x = -7/-4, the minuses cancel each other out, so basically,

    x= 7/4

    Is this the type of simplification that you mean? Or have I misunderstood the point?


    Point taken, wrong type of math. :shiftyrun:

    Sorry guys, please don't mind this post!
    Offline

    0
    ReputationRep:
    (3x-7)(x-1)= 0...

    Then carry on...
    Offline

    7
    ReputationRep:
    (Original post by Farhan.Hanif93)
    Quadratic formula or complete the square? (I suggest the former)

    Are you aware of those techniques?
    This


    (Original post by Tizmo)
    Basically, simply all that you can in the first step.

    3x*2 - 10x +7 = 0 will become
    6x -10x +7 = 0, which will become
    -4x + 7 = 0, which will become
    -4x = -7, so
    x = -7/-4, the minuses cancel each other out, so basically,

    x= 7/4

    Is this the type of simplification that you mean?
    NOT this :O
    • Thread Starter
    Offline

    14
    ReputationRep:
    yes but I didn't think these would be necessary this is a differentiation question. Thanks.
    Offline

    0
    ReputationRep:
    Not what Tizmo said!

    I'll carry on then...

    if the above is true then x=1 or x=7/3
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Tizmo)
    Basically, simply all that you can in the first step.

    3x*2 - 10x +7 = 0 will become
    6x -10x +7 = 0, which will become
    -4x + 7 = 0, which will become
    -4x = -7, so
    x = -7/-4, the minuses cancel each other out, so basically,

    x= 7/4

    Is this the type of simplification that you mean? Or have I misunderstood the point?
    you sir have misread the question that 3x is raised to the power of two not multiplied by 2

    3x squared, not 3x*2
    Offline

    17
    ReputationRep:
    (Original post by Tizmo)
    Basically, simply all that you can in the first step.

    3x*2 - 10x +7 = 0 will become
    6x -10x +7 = 0, which will become
    -4x + 7 = 0, which will become
    -4x = -7, so
    x = -7/-4, the minuses cancel each other out, so basically,

    x= 7/4

    Is this the type of simplification that you mean? Or have I misunderstood the point?
    Firstly, please don't post full solutions, it's against the way we post help on here.

    Secondly, make sure you understand what you're helping with before posted otherwise that could lead to further confusion.

    (Original post by birduk)
    (3x-7)(x-1)= 0...

    Then carry on...
    The question asks you to make x the subject first so factorising is not the way to go.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by birduk)
    Not what Tizmo said!

    I'll carry on then...

    if the above is true then x=1 or x=7/3
    thanks how do you come to that? I'm not very good at factorising with things that have coefficients of x :P
    Offline

    7
    ReputationRep:
    (Original post by kingkongjaffa)
    thanks how do you come to that? I'm not very good at factorising with things that have coefficients of x :P
    Use the quadratic formula then, it always works!
    Offline

    18
    ReputationRep:
    is this for c2? i have a funny feeling i recognise this question and if so its in differentiation and you do have to factorise the quadratic
    • Thread Starter
    Offline

    14
    ReputationRep:
    No birduk is right by make the subject i didnt mean in that sense sorry for the confusion.
    • Thread Starter
    Offline

    14
    ReputationRep:
    ya it is
    Offline

    0
    ReputationRep:
    Sorry guys, totally misread the question!

    Please don't mind my post.
    Offline

    7
    ReputationRep:
    (Original post by Tizmo)
    Sorry guys, totally misunderstood the question!

    Please don't mind my post.
    *misread
    Offline

    0
    ReputationRep:
    (Original post by eliotball)
    *misread
    What I meant to say. Cheers mate.
    Offline

    2
    ReputationRep:
    (Original post by kingkongjaffa)
    hey guys I have a question

    if I have 3x^2 -10x +7 = 0

    how do I make x the subject and hence find x ?

    first I made it : 3x^2 -10x = -7

    but I don't know how to rearrange this algebraically
    Factorise...

    3x^2-10x +7 = 0

    ac = 21

    (3x^2 -3x) (-7x + 7)=0

    3x(x-1) -7(x -1) = 0

    (3x - 7) (x-1) =0

    x = 7/3 and x = 1
    Offline

    7
    ReputationRep:
    (Original post by Tizmo)
    What I meant to say. Cheers mate.
    No problem, I'm sure you had good intentions posting that solution, it was just a pretty awful mistake :P
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by crazycake93)
    Factorise...

    3x^2-10x +7 = 0

    ac = 21

    (3x^2 -3x) (-7x + 7)=0

    3x(x-1) -7(x -1) = 0

    (3x - 7) (x-1) =0

    x = 7/3 and x = 1
    ooh can you explain this please firstly AC is 3*7 but can you explain why you did that.
    secondly can you explain how you go from 3x(x-1) -7(x-1) to (3x-7) (x-1)?
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 21, 2011
The home of Results and Clearing

2,341

people online now

1,567,000

students helped last year

University open days

  1. London Metropolitan University
    Undergraduate Open Day Undergraduate
    Sat, 18 Aug '18
  2. Edge Hill University
    All Faculties Undergraduate
    Sat, 18 Aug '18
  3. Bournemouth University
    Clearing Open Day Undergraduate
    Sat, 18 Aug '18
Poll
A-level students - how do you feel about your results?
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

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.