# Equation of circles

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• Nov 24th 2012, 01:24 AM
Thorpelizts
Equation of circles
So, I've attached both the question and my working inside.

for part 1, I'm not sure how to get the radius and for part 2, how to get the point?
• Nov 24th 2012, 01:31 AM
Prove It
Re: Equation of circles
Quote:

Originally Posted by Thorpelizts
So, I've attached both the question and my working inside.

for part 1, I'm not sure how to get the radius and for part 2, how to get the point?

In part 1, complete the square on the x terms and complete the square on the y terms. Then move any extra constants to the right. You should then be able to write the equation in the form \displaystyle \displaystyle \begin{align*} (x - h)^2 + (y -k )^2 = r^2 \end{align*}.

As for part b), the y axis is where x = 0, so let x = 0 in your equation and solve for y.
• Nov 24th 2012, 01:35 AM
MarkFL
Re: Equation of circles
I didn't look at your work, I don't care for images of hand-written work.

We are given the equation:

$\displaystyle x^2+y^2-6x-8y+16=0$

You want to complete the square on the two variables:

$\displaystyle (x^2-6x+9)+(y^2-8y+16)=-16+9+16$

Now, you want to get this into the form:

$\displaystyle (x-h)^2+(y-k)^2=r^2$

where the center is at $\displaystyle (h,k)$ and the radius is $\displaystyle r$.

Can you proceed?

For part b), what is the equation of the $\displaystyle y$-axis?

edit: sorry, I didn't see your post Prove It.