# Thread: Question on coordinate geometry of circles

1. ## Question on coordinate geometry of circles

Hi, I'm currently doing AS-level Maths in the UK, and I'm struggling with this question on coordinate geometry of circles:

A circle passes through the points (0, -3) and (0, 3) and has radius 5. Draw a sketch to show the two possible positions of the circles and find their equations.

Any help would be greatly appreciated!

2. Originally Posted by sakuraxkisu
Hi, I'm currently doing AS-level Maths in the UK, and I'm struggling with this question on coordinate geometry of circles:

A circle passes through the points (0, -3) and (0, 3) and has radius 5. Draw a sketch to show the two possible positions of the circles and find their equations.

Any help would be greatly appreciated!
Things we know. The equation of a circle is given by the formula

$\displaystyle (x-h)^2+(y-k)^2=r^2$ Since we know r we get

$\displaystyle (x-h)^2+(y-k)^2=25$
Since we know two points that lie on the circle we can plug them in for (x,y) and this will give a system of equations in two unknowns that you can solve for h and
k.

Can you finish from here?

3. Thank you! I was on the right tracks, with the substitution of (0, -3) and (0, 3) into the equation, but thank you for clarifying