Re: Cicle word problem

On 18 Jan, 19:57, quasi <qu...@xxxxxxxx> wrote:
On Sun, 18 Jan 2009 11:39:35 -0800 (PST), newbar...@xxxxxxxxx wrote:
Hi,

Still working through my maths book and the question I'm currently
having problems with this one:

"The line joining A(5,3) and B(4,-2) is a diameter of a circle. If P
(a,b) is a point on the circumference find a relationship between a
and b".

I thought finding the centre of the circle and the radius might be a
good starting point and came up with (9 / 2,1 / 2), and sqrt(6 1/2)
respectively. I didn't really know how to proceed so thought I'd have
a look at the answer and attempt to work back from there!

The answer is

a^2 + b^2 - 9a - b + 14 = 0.

Now I don't see my midpoint/radius in there (directly) so I'm confused
as to what I was supposed to do to arrive at the answer. Help please!

You are supposed to already know the equation of a circle with center
(h,k) and radius r. Thus, in this case, what is the equation?

Then, since the point (a,b) is on the circle, it must satisfy the
equation. Thus, you get an equation involving a and b.

Rework the new equation so as to match the book answer.

quasi- Hide quoted text -

- Show quoted text -


Hi quasi,

Thanks for throwing me a lifeline. (You've helped me before too).

I am aware of the existence of an equation for circles (but don't know
it - will look it up). The book's not mentioned the equation yet so I
figured they might want me to determine the relationship without using
that directly.

I'll follow your advice and will let you know how I get on.

Thanks,

Pete

Regards,

Pete
.

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