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#1 2006-03-08 05:18:40
- RickyOswaldIOW
- Member
- Registered: 2005-11-18
- Posts: 212
Equation of a Circle.
This circle has a center point at (1, 2) and a radius of 3.
According to the genral equation of a circle, that's:
(x - 1)² + (y - 2)² = 3²
expanded:
x² - 2x + 1 + y² - 4y + 4 = 9
and
x² - 2x + y² - 4y = 4?
my book is saying (y - 2) (y - 2) = y² - 2√2y!
(y - 2) (y - 2) = y² - 2y - 2y + 4 in my eyes?!
Aloha Nui means Goodbye.
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#2 2006-03-08 12:50:57
- Ansette
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- Registered: 2006-02-19
- Posts: 21
Re: Equation of a Circle.
must be a mistake in the book...
the equation u have is indeed correct..
im curious as to why ur looking at (y-2)²...?
the x²-2x can be simplified to x(x-2)
so:
x(x-2) +y²-4y=4
what it seems you're doing is saying (y-2)² = y²-4y+4.. which is true..
however what you have in this equation is:
x(x-2) = -y²+4y+4
which using the quadratic formula forms:
y=1±√2
so you have x(x-2) = (y-[1+√2])(y-[1-√2])
or aternatively:
x(x-2) = (y-[1+√2])(y+[√2-1])
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#3 2006-03-09 05:14:23
- RickyOswaldIOW
- Member
- Registered: 2005-11-18
- Posts: 212
Re: Equation of a Circle.
im curious as to why ur looking at (y-2)²...?
My question asks "Give the equation of a circle with center (1, 2), radius 3"
and the genral equation for a circle is "(x - a)² + (y - b)² = r²"
hence (y - 2)².
From that question, the book states that the answer is;
(x - 1)² + (y - √2)² = 3
expanded
x² - 2x + y² - 2√2y = 0
very bizarre!
Aloha Nui means Goodbye.
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#4 2006-03-09 05:28:52
- Ansette
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- Registered: 2006-02-19
- Posts: 21
Re: Equation of a Circle.
if this is alevel im presuming it's edexcel.. there are a lot of mistakes in the answers bit lol
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#5 2006-03-10 05:14:36
- RauLiTo
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- From: Bahrain
- Registered: 2006-01-11
- Posts: 142
Re: Equation of a Circle.
that is our lesson 
cool
well explain your question more and u will get the answer 
ImPo$$!BLe = NoTH!nG
Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...
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#6 2006-03-11 00:34:10
- amonjezi
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- Registered: 2006-03-09
- Posts: 9
Re: Equation of a Circle.
must be mistakes in your books
what is your name book
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#7 2006-03-13 10:49:00
- RickyOswaldIOW
- Member
- Registered: 2005-11-18
- Posts: 212
Re: Equation of a Circle.
It is indeed edexcel A-level. The book is Core 2 and I study through the National Extensions College.
Aloha Nui means Goodbye.
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