Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    A tangent is drawn from (8,2) to touch the circle x^2+y^2-4x-8y-5=0

    A) Find the radius of the circle

    This is fairly straight forward, as I know that when I complete the square I will get the radius squared as 25, then square rooting it will give me 5. So radius = 5

    By completing the square I get

    So the equation of the circle is (x-2)^2+(y-4)^2 = 25
    (x-2)+(y-4) = 5

    So centre is (2,4) and radius is 5

    Part B) Find the length of the tangent

    I know that you have to use pythagoras for it and use the points however, I do not fully know understand how to do it. So I was wondering If you could fully explain me how to find the length of the tangent
    Offline

    12
    ReputationRep:
    Find out the lenght from the point to the center of the circle. (x1,y1) (x2,y2) has distance ((x1-x2)^2+(y1-y2)^2)^0.5
    Now draw a picture and notice where the right angle is
    Offline

    16
    ReputationRep:
    Sketch a diagram and think about where you have a right angle
    Offline

    20
    ReputationRep:
    Yes you do Pythagoras... the distance between (2,4) & (8,2) is the hypotenuse and the radius is one of the short sides.
    Offline

    12
    ReputationRep:
    (Original post by abdul95)
    A tangent is drawn from (8,2) to touch the circle x^2+y^2-4x-8y-5=0

    A) Find the radius of the circle

    This is fairly straight forward, as I know that when I complete the square I will get the radius squared as 25, then square rooting it will give me 5. So radius = 5

    By completing the square I get

    So the equation of the circle is (x-2)^2+(y-4)^2 = 25
    (x-2)+(y-4) = 5

    So centre is (2,4) and radius is 5

    Part B) Find the length of the tangent

    I know that you have to use pythagoras for it and use the points however, I do not fully know understand how to do it. So I was wondering If you could fully explain me how to find the length of the tangent
    That is incorrect btw (see bold).

    Anyway, you have to plot the points and there will be a triangle on which you can use pythagoras.
    Offline

    14
    ReputationRep:
    This is C2?
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: October 1, 2011

University open days

  • Heriot-Watt University
    School of Textiles and Design Undergraduate
    Fri, 16 Nov '18
  • University of Roehampton
    All departments Undergraduate
    Sat, 17 Nov '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 17 Nov '18
Poll
Have you ever experienced bullying?
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.