x Turn on thread page Beta
 You are Here: Home >< A-levels

# Circles Past Paper questions watch

1. Hey!
I have been sat here trying this question for at least 2 hours and tried everything I can think of...any ideas? (it's part b I am stuck on, but I will put entire question up)

Question: The circle C has centre A and equation x^2+y^2+4x-8y+10=0
a)find the coordinates of A and the radius of C
b)The line L has equation x-3y+4=0
Show that L is a tangent to circle C
2. (Original post by alicebrr)
Hey!
I have been sat here trying this question for at least 2 hours and tried everything I can think of...any ideas? (it's part b I am stuck on, but I will put entire question up)

Question: The circle C has centre A and equation x^2+y^2+4x-8y+10=0
a)find the coordinates of A and the radius of C
b)The line L has equation x-3y+4=0
Show that L is a tangent to circle C
to show that something is a tangent you must put the equation of the line into the equation of the circle and show that it only meets the circle at one point. If this is the case it will usually factorize into 2 identical brackets
3. (Original post by alicebrr)
Hey!
I have been sat here trying this question for at least 2 hours and tried everything I can think of...any ideas? (it's part b I am stuck on, but I will put entire question up)

Question: The circle C has centre A and equation x^2+y^2+4x-8y+10=0
a)find the coordinates of A and the radius of C
b)The line L has equation x-3y+4=0
Show that L is a tangent to circle C
so for part b i would make y the subject of the equation of the line, put it into the equation of the circle, expand and simplify, make it equal 0 and it should factorise into 2 identical brackets from which you can say that because there is only 1 solution that it is a tangent
4. part a)

expand

( x - a )2 + ( y - b )2 = r2

and compare to your version to find a,b,r
5. (Original post by Bored123454321)
so for part b i would make y the subject of the equation of the line, put it into the equation of the circle, expand and simplify, make it equal 0 and it should factorise into 2 identical brackets from which you can say that because there is only 1 solution that it is a tangent
Got you! So it would be something like this...? Yes?
Attached Images

6. (Original post by alicebrr)
Got you! So it would be something like this...? Yes?
^^ looks about right
7. (Original post by thefatone)
^^ looks about right
Thank you! I had that part at least an hour ago ahh
8. To show tangency, just show that the discriminant of the quadratic formed is 0 line is tangent to curve.

Turn on thread page Beta
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 28, 2016
Today on TSR

### Happy St Patrick's day!

How are you celebrating?

### Stay at sixth form or go to college?

Discussions on TSR

• Latest
Poll
Help with your A-levels

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Uni match

Our tool will help you find the perfect course for you

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Degrees without fees

Discover more about degree-level apprenticeships.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets

## Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest

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