# Circle Maths help.Watch

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#1
Got a example question in a lecture today and I don't understand it. Could someone help please?

I need to find the center and the radius of this circle.
x^2-4x+y^2+10y-7=0

so I was told that this was how it goes...
(x^2-4x+4)+(y^2+10y+25)=7+4+25

(x-2)^2+(y+5)^2=36

6^2=36

But I don't understand where the +4 and the +25 come from in the first line of working. Any help appreciated.
0
5 years ago
#2
(Original post by Guru Jason)
Got a example question in a lecture today and I don't understand it. Could someone help please?

I need to find the center and the radius of this circle.
x^2-4x+y^2+10y-7=0

so I was told that this was how it goes...
(x^2-4x+4)+(y^2+10y+25)=7+4+25

(x-2)^2+(y+5)^2=36

6^2=36

But I don't understand where the +4 and the +25 come from in the first line of working. Any help appreciated.

This is A Level, not undergraduate

But the bit you are asking about is Completing the Square which is GCSE knowledge

Do you know that

and, therefore, that

1
#3
(Original post by TenOfThem)
This is A Level, not undergraduate

But the bit you are asking about is Completing the Square which is GCSE knowledge

Do you know that

and, therefore, that

Thanks. It's a foundation year so I suppose it would be A level.
0
5 years ago
#4
(Original post by Guru Jason)
Thanks. It's a foundation year so I suppose it would be A level.
Ah - ok

So did you understand what I said or do you want me to go slower
0
#5
(Original post by TenOfThem)
Ah - ok

So did you understand what I said or do you want me to go slower
I think I got it now. I should be able to do the rest (the radius bit) of the questions now. Thanks.
0
5 years ago
#6
(Original post by Guru Jason)
I think I got it now. I should be able to do the rest (the radius bit) of the questions now. Thanks.
ok
0
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