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#1 2018-03-31 01:44:53
- Monox D. I-Fly
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- From: Indonesia
- Registered: 2015-12-02
- Posts: 2,000
[ASK] Circle Equation
A circle L is going through the point O (0, 0) and P (6, 0). The center is in the line
. The equation of the circle L is ....A.
B.
C.
D.
E.
Since the equation of a circle is
, I substituted both known points to the equation and got C = 0 as well as B = -6, so the answer is obviously B. But then my student asked "What if all options have -6 as their B? How would we know the answer?". I think it has something to do with that , but how? Please give me some hints.Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away.
May his adventurous soul rest in peace at heaven.
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#2 2018-03-31 04:59:15
- Bob
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Re: [ASK] Circle Equation
OP is a chord so the centre also lies on x=3. Intersect that with the other line to determine the centre and then the radius.
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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#3 2018-03-31 12:14:13
- Monox D. I-Fly
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- From: Indonesia
- Registered: 2015-12-02
- Posts: 2,000
Re: [ASK] Circle Equation
Okay, I found the center (3, 4) and the radius 5 by Pythagoras. That means the equation is:
Last edited by Monox D. I-Fly (2018-03-31 12:16:46)
Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away.
May his adventurous soul rest in peace at heaven.
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#4 2018-03-31 19:54:21
- Bob
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- Registered: 2010-06-20
- Posts: 10,640
Re: [ASK] Circle Equation
Yes.
B
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#5 2018-03-31 23:50:53
- Alg Num Theory
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- Registered: 2017-11-24
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Re: [ASK] Circle Equation
A.
B.
C.
D.
E.
The only one of these that has the point (6,0) lying on it is B – so that must be the answer. No need for any working.
See? If you use your brain a little bit more, you can save yourself a whole lot of time and hard work for nothing.
Me, or the ugly man, whatever (3,3,6)
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#6 2018-04-01 00:47:16
- Bob
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Re: [ASK] Circle Equation
In post 1, Monox does exactly that but then goes on to ask what if one couldn't deduce an answer from the multi choice answers. I think it's worth considering such things as it improves one's techniques.
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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