Join TSR now and get all your revision questions answeredSign up now

C1 circles help Watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    I don't understand the very last part to these questions, 'Find the values of k for which the line is a tangent to the circle'.

    I've worked out that k = -3/4 and k = 4/3.. if i put these into the line equation I get Y = -3/4x + 6 and y = 4/3X + 6.. how do I know these lines are tangents to the circle?

    Name:  k.JPG
Views: 86
Size:  49.1 KB
    Offline

    2
    ReputationRep:
    (Original post by tom472)
    I don't understand the very last part to these questions, 'Find the values of k for which the line is a tangent to the circle'.

    I've worked out that k = -3/4 and k = 4/3.. if i put these into the line equation I get Y = -3/4x + 6 and y = 4/3X + 6.. how do I know these lines are tangents to the circle?

    Name:  k.JPG
Views: 86
Size:  49.1 KB
    You've found the equation for where they intersect. And then you've found an equation in k when these have 1 repeated root. Do you remember what one repeated root means?


    Say if I gave you a regular quadratic with 1 repeated root (b^2 - 4ac = 0) how would you describe what that graph looks like?
    • Thread Starter
    Offline

    0
    ReputationRep:
    If it had one repeated root does that mean it touches the x axis once? Sorry I still don't get how I know theyre tangents
    Offline

    2
    ReputationRep:
    (Original post by tom472)
    If it had one repeated root does that mean it touches the x axis once? Sorry I still don't get how I know theyre tangents
    Yep that's right. So if we've made this straight line and this circle equal (by subbing in for y like you did) and they only have one repeated root then the same thing applies; the line only 'touches' the circle i.e. it's a tangent.
    Offline

    0
    ReputationRep:
    (Original post by hassi94)
    Yep that's right. So if we've made this straight line and this circle equal (by subbing in for y like you did) and they only have one repeated root then the same thing applies; the line only 'touches' the circle i.e. it's a tangent.
    How do you do 7)d)i?
    Offline

    2
    ReputationRep:
    (Original post by GreenLantern1)
    How do you do 7)d)i?
    sub y = kx + 6 into the equation of the circle, expand and simplify.
    Offline

    0
    ReputationRep:
    (Original post by hassi94)
    sub y = kx + 6 into the equation of the circle, expand and simplify.
    Ahh I see know, cheers
 
 
 
Poll
Is GoT overrated?
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

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