You are Here: Home >< Maths

# Circle intersection question Watch

1. Q. the circle x^2 + y^2 = 20 intersects the line y = x -2 at the point A and B
a) work out the coordinates of A and B
b) work out the length of AB

(I am stuck on part a :P )
2. Solve a pair of simultaneous equations.

Spoiler:
Show
Square the equation of the line. Substitute for in the equation of the circle.
3. For part a) I would input (x-2) into the circle equation to get x^2 + (x-2)^2 = 20 and then solve for x. Then I would just input the values of x into y = x-2 to get y
4. If you simply the equation
it will be x^2 - 2x - 9 = 0
correct ?
5. (Original post by aking144)
If you simply the equation
it will be 2x^2 - 2x - 9 = 0
correct ?
I don't believe so.
6. (Original post by joostan)
I don't believe so.
I'm confused
could some do a trial run ?
7. (Original post by aking144)
I'm confused
could some do a trial run ?
Post what you did, and I will attempt to find where you're going wrong.
We're not meant to provide solutions unless it is absolutely necessary
8. (Original post by joostan)
Post what you did, and I will attempt to find where you're going wrong.
We're not meant to provide solutions unless it is absolutely necessary
ok

x^2 + ( x - 2 )^2 = 20
- 2x^2 - 4x + 2 = 20
- 2x^2 -4x -18
- x^2 - 2x - 9 = 0
thats what i have done so far
But the answer is an integer
9. (Original post by aking144)
ok

x^2 + ( x - 2 )^2 = 20
=>2x^2 - 4x + 2 = 20
=>2x^2 -4x -18
=>x^2 - 2x - 9 = 0
thats what i have done so far
But the answer is an integer
Arrows are better than - signs when saying that something implies something else.
And what is (-2)2
10. (Original post by joostan)
Arrows are better than - signs when saying that something implies something else.
And what is (-2)2
lol making all the mistakes on the net lol
11. (Original post by aking144)
ok

x^2 + ( x - 2 )^2 = 20
- 2x^2 - 4x + 2 = 20
- 2x^2 -4x -18
- x^2 - 2x - 9 = 0
thats what i have done so far
But the answer is an integer
You haven't multiplied it out right, it should come out like this:

x^2 + (x^2 - 4x + 4) = 20

2x^2 - 4x + 4 = 20

2x^2 - 4x - 16 = 0

You then factorise the equation to get (2x - 8)(x + 2) = 0

So 2x - 8 = 0 and x + 2 = 0

2x = 8

x = 4

Therefore x = 4 and x = -2

To find y you just put these two values of x into y = x - 2.
12. (Original post by aking144)
lol making all the mistakes on the net lol
No worries - post again if you get any more problems.
13. thanks it really helps

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: April 4, 2013
Today on TSR

### Am I pregnant?

...or just paranoid?

### Have I ruined my eyebrows

Discussions on TSR

• Latest
• ## 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
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## 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

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