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

    11
    ReputationRep:
    (Original post by madfish)
    No! I am not winding you up! dont worry

    But yea, I know that... but where do I get these numbers?!! there are no coordinates in the question or anything?? Eugh, i give up on this, ill move onto the next question on the book...
    Can you find a relationship between (1,1) ; (2,2) ; (3,3) ... (n,n)?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    Ok, I will tell you the answer - not that it's going to help you.

    For the circle to 'touch' each axis we must have that the centre point of the circle is of the form (a,b) where a=b

    Since we also have that (a,b) lies on the line y=3x-4 we must have b=3a-4 but we also know that a=b, so a = 3a -4 gives the centre of the circle being (2,2) now the radius is also obvious.
    I understand it now, that was more helpful than all the other posts combined.

    Thanks
    Offline

    17
    ReputationRep:
    (Original post by madfish)
    I understand it now, that was more helpful than all the other posts combined.

    Thanks
    No it wasn't. You think it was helpful because I told you the answer, you need to learn to think for yourself - you're going to be royally screwed in AS Maths exams in all honesty.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    Ok, I will tell you the answer - not that it's going to help you.

    For the circle to 'touch' each axis we must have that the centre point of the circle is of the form (a,b) where a=b

    Since we also have that (a,b) lies on the line y=3x-4 we must have b=3a-4 but we also know that a=b, so a = 3a -4 gives the centre of the circle being (2,2) now the radius is also obvious.
    why are we allowed to set b equal to 3a-4?
    Offline

    17
    ReputationRep:
    (Original post by madfish)
    why are we allowed to set b equal to 3a-4?
    Because it lies on the line y=3x-4
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    No it wasn't. You think it was helpful because I told you the answer, you need to learn to think for yourself - you're going to be royally screwed in AS Maths exams in all honesty.
    But I now understand it as you showed me how to arrive at the answer, I have thought about it
    Offline

    18
    ReputationRep:
    (Original post by Noble.)
    Because it lies on the line y=3x-4
    I think he means why do we have the x co ordinate = to the y coordinate?

    Is the centre the origin?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by joostan)
    Can you find a relationship between (1,1) ; (2,2) ; (3,3) ... (n,n)?
    yep, the x and y coordinates are equal distance from the axis
    Offline

    11
    ReputationRep:
    (Original post by madfish)
    yep, the x and y coordinates are equal distance from the axis
    OK so can you see how this is a requirement for the circle? The centre must be equidistant from the x-axis and the y-axis?
    Offline

    17
    ReputationRep:
    (Original post by madfish)
    But I now understand it as you showed me how to arrive at the answer, I have thought about it
    Yes, but this was for a specific case, unless you get the identical question, you're probably not going to know how to do it. How about this, it's essentially the exact same question:

    "A circle touches the negative y-axis and the negative x-axis and it's centre lies on the line y=5x+7. What is the equation of the circle?"
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    Yes, but this was for a specific case, unless you get the identical question, you're probably not going to know how to do it. How about this, it's essentially the exact same question:

    "A circle touches the negative y-axis and the negative x-axis and it's centre lies on the line y=5x+7. What is the equation of the circle?"
    b=5a+7 but since they are equal distance form the axis then a=5a+7 therefore a=-7/4 and b=-7/4


    job done
    Offline

    17
    ReputationRep:
    (Original post by madfish)
    b=5a+7 but since they are equal distance form the axis then a=5a+7 therefore a=-7/4 and b=-7/4


    job done
    Where's the equation of the circle? :lol:
    Offline

    18
    ReputationRep:
    (Original post by Noble.)
    Where's the equation of the circle? :lol:
    My turn for questions...

    Why is it an equal distance from both sets of axis? (x=y)

    The centre isn't the origin?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    Where's the equation of the circle? :lol:
    sorry forgot that part :P

    It would be (x+7/4)^2 + (y+7/4)^2 = 49/16 ??
    Offline

    17
    ReputationRep:
    (Original post by L'Evil Fish)
    My turn for questions...

    Why is it an equal distance from both sets of axis? (x=y)

    The centre isn't the origin?
    Because it just touches both axes, so the centre point must satisfy x=y, otherwise the circle would 'overhang' one of the axes, or not touch it.
    Offline

    18
    ReputationRep:
    (Original post by Noble.)
    Because it just touches both axes, so the centre point must satisfy x=y, otherwise the circle would 'overhang' one of the axes, or not touch it.
    oh, it lies on them?

    I thought it just crossed over it like one tiny part of it
    Offline

    17
    ReputationRep:
    (Original post by L'Evil Fish)
    oh, it lies on them?

    I thought it just crossed over it like one tiny part of it
    Generally when it says 'touches' it means just at one point.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Noble.)
    Generally when it says 'touches' it means just at one point.
    Was the equation right?

    do you mind asking me some more c2 circle questions? I just find I try a lot harder in them if I am doing them for someone else... only if you don't mind
    Offline

    18
    ReputationRep:
    (Original post by Noble.)
    Generally when it says 'touches' it means just at one point.
    That makes a lot more sense now :facepalm: sorry about that
    Offline

    17
    ReputationRep:
    (Original post by madfish)
    Was the equation right?

    do you mind asking me some more c2 circle questions? I just find I try a lot harder in them if I am doing them for someone else... only if you don't mind
    Given that the radius r is a solution to x^2 + x - 7 = 0 and the point (1,2) lies on the circle and given that all points (p,q) on the circle are positive, that is p >0 and q>0 what conditions must we put on the centre of the circle (a,b) to ensure a circle satisfies all these things?
 
 
 
  • 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
    Have you ever participated in a Secret Santa?
    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

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