Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    3
    ReputationRep:
    Question:

    Find equation of the line joining following points:

    (-3,4)(-3,9)

    So I found gradient or rather I didnt - ifyou find the gradient is it not infinity? 5/0...

    If I found a normal number I'd then do:

    y - y1 = m(x - x1)

    But I cant get that with infinity.

    The answer in the book is:

    x + 3 = 0
    Offline

    0
    ReputationRep:
    plot the points on an xy plane
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Pheylan)
    plot the points on an xy plane
    Ok I see the gradient is zero but then how do you possibly get x + 3?
    Offline

    15
    ReputationRep:
    Is it even possible to use the y -y1 = m (x - x1) formula for that?

    You see, with the points (-3,4) and (-3,9), it should be fairly clear to you that the it would be a vertical line passing through x = -3, hence, the answer.
    Offline

    15
    ReputationRep:
    Vertical lines (x = constant) can't be put into the form

    y = mx+c

    The most general form of a line's equation is

    ax+by+c=0
    Offline

    13
    ReputationRep:
    The line is vertical. You can still provide an equation for it though, it just won't be in the form y=mx+c.
    Offline

    2
    ReputationRep:
    (Original post by Dededex)
    Ok I see the gradient is zero but then how do you possibly get x + 3?
    Have you done transforming graphs yet?

    You need to understand that the line x=0 have been shifted 3 units in the negative x-direction. When going that direction you have to ADD the units. Therefore x + 3 = 0

    (When going the positive x-direction, you need to SUBTRACT the units, so if the points were (3, 4) and (3, 9) then the graph would be x - 3 = 0)

    EDIT:

    I just realised the line is just x = -3 where they've brought over the 3. You don't need to do all that but it's good practice :P:
    Offline

    15
    ReputationRep:
    (Original post by Dededex)
    Ok I see the gradient is zero but then how do you possibly get x + 3?
    gradient is infinite, not zero
    Offline

    14
    ReputationRep:
    It's a straight line... try plotting it on a graph if you can't see it
    It goes through (-3) , so it's the line x=-3 (or x+3=0 )
    You don't have to do what you did above
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.