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#1 2006-03-09 04:18:40

RickyOswaldIOW
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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) + (y - 2) = 3

expanded:
x - 2x + 1 + y - 4y + 4 = 9

and
x - 2x + y - 4y = 4?

my book is saying (y - 2) (y - 2) = y - 2√2y!
(y - 2) (y - 2) = y - 2y - 2y + 4 in my eyes?!


Aloha Nui means Goodbye.

#2 2006-03-09 11:50:57

Ansette
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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)...?

the x-2x can be simplified to x(x-2)

so:

x(x-2) +y-4y=4

what it seems you're doing is saying (y-2) = y-4y+4.. which is true..

however what you have in this equation is:

x(x-2) = -y+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])

#3 2006-03-10 04:14:23

RickyOswaldIOW
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Re: Equation of a Circle.

im curious as to why ur looking at (y-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) + (y - b) = r"
hence (y - 2).

From that question, the book states that the answer is;
(x - 1) + (y - √2) = 3
expanded
x - 2x + y - 2√2y = 0

very bizarre!


Aloha Nui means Goodbye.

#4 2006-03-10 04:28:52

Ansette
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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

#5 2006-03-11 04:14:36

RauLiTo
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Re: Equation of a Circle.

that is our lesson big_smile cool
well explain your question more and u will get the answer wink


ImPo$$!BLe = NoTH!nG
Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

#6 2006-03-11 23:34:10

amonjezi
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Re: Equation of a Circle.

must be mistakes in your books
what is your name book

#7 2006-03-14 09:49:00

RickyOswaldIOW
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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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