The Student Room Group

Length of AB with a circle and a tangent

The circle (x-1)^2 + (y-1)^2=4 has a tangent at point A that also passes through the point B (6, 0). Find distance AB. Really struggling with this question, can anyone show me the method?
Hint: draw apicture…the tangent to a circle is perpendicular to the radius …. Pythagoras….

Question came with a hint
Original post by LukeMontgomery
The circle (x-1)^2 + (y-1)^2=4 has a tangent at point A that also passes through the point B (6, 0). Find distance AB. Really struggling with this question, can anyone show me the method?
Hint: draw apicture…the tangent to a circle is perpendicular to the radius …. Pythagoras….

Question came with a hint


What does the sketch you've drawn show? Which two side do you know the length of already (one of which has to be worked out?)
Original post by SeanFM
What does the sketch you've drawn show? Which two side do you know the length of already (one of which has to be worked out?)


All I know is that the centre of the circle is 1,1 and the radius is 2, I don't understand how to work out the equation of the tangent that goes through 6,0.
Original post by LukeMontgomery
All I know is that the centre of the circle is 1,1 and the radius is 2, I don't understand how to work out the equation of the tangent that goes through 6,0.


If we call C the centre of the circle and CAB the triangle you're interested in... AB is the length we want. What is CA? What is CB? What can we do with those things?
Original post by SeanFM
If we call C the centre of the circle and CAB the triangle you're interested in... AB is the length we want. What is CA? What is CB? What can we do with those things?


Are you trying to help me through it or do you not understand either, difficult to tell through text!
Original post by LukeMontgomery
Are you trying to help me through it or do you not understand either, difficult to tell through text!


I'm asking you questions to help you help yourself. Are you with me and my hits so far?
Original post by SeanFM
I'm asking you questions to help you help yourself. Are you with me and my hits so far?


Is the answer root 26? 5^2 + 1^2=26 then square root 26?
Original post by LukeMontgomery
Is the answer root 26? 5^2 + 1^2=26 then square root 26?


Yes one side is root 26, what is the other known side
Original post by AlexS101
Yes one side is root 26, what is the other known side


Didn't I just state all 3 sides, 5,1, and root 26, I feel like im missing something.
Original post by LukeMontgomery
Is the answer root 26? 5^2 + 1^2=26 then square root 26?


That's the length of CB, which we need but isn't the final answer? Can you see why it's useful and what to do next?
Original post by SeanFM
That's the length of CB, which we need but isn't the final answer? Can you see why it's useful and what to do next?


Length CB is what I thought was root 26.
Original post by LukeMontgomery
Length CB is what I thought was root 26.


Correct. If you look at the diagram you've sketched you'll see what CB is (C is the centre of the circle, B is the given point and CB is the line between them, and ABC forms a right-angled triangle. Which side are you looking for in the question? What two sides do you know now? (One is CB). So where do you go from there?
Original post by SeanFM
Correct. If you look at the diagram you've sketched you'll see what CB is (C is the centre of the circle, B is the given point and CB is the line between them, and ABC forms a right-angled triangle. Which side are you looking for in the question? What two sides do you know now? (One is CB). So where do you go from there?


You're looking for the tangent line, I know CB and CA, I don't know where you go from there.
Original post by LukeMontgomery
You're looking for the tangent line, I know CB and CA, I don't know where you go from there.


You're almost there :borat:

SO ABC is a right angled triangle.. you've got CB and CA... you want AB...
Original post by SeanFM
You're almost there :borat:

SO ABC is a right angled triangle.. you've got CB and CA... you want AB...


Is it root 26 squared (so 26) - 2 squared (4) = 22 length is root 22?
Original post by LukeMontgomery
Is it root 26 squared (so 26) - 2 squared (4) = 22 length is root 22?


Yes, that should be correct. Well done :smile:
Original post by SeanFM
Yes, that should be correct. Well done :smile:


Would it be ok if you could right out the whole method, its ok if you don't, now that I understand it!
Original post by LukeMontgomery
Would it be ok if you could right out the whole method, its ok if you don't, now that I understand it!


If you look back at my previous hints you'll probably be able to piece it together, along with the hints already given in the question.
Original post by SeanFM
If you look back at my previous hints you'll probably be able to piece it together, along with the hints already given in the question.


Ok, cheers, never thought I could do this question, thank god for this website! Couldn't find anything anywhere else.
That was pretty epic support


Posted from TSR Mobile

Quick Reply

Latest