# Homework Help: Find the equation of the circle

1. Sep 30, 2010

### zorro

1. The problem statement, all variables and given/known data
Find the equation of the circle which touches the axes and whose centre lies on the line x-2y=3

2. Relevant equations

3. The attempt at a solution

The given line passes through 1st, 3rd and 4th quadrants.
So the centre of the circle may lie in any of these i.e. it can be of the form (a,a) (a,-a) (-a,-a).
But my book considers only (a,a) (a,-a) for finding the equation of circles.

2. Sep 30, 2010

### Mentallic

Re: Circles

for the line $$y=x/2-3/2$$ even though it passes through the first quadrant, it doesn't intersect the line y=x, x>0 so there cannot exist a circle with centre on that line which touches both x and y axes.

3. Sep 30, 2010

### zorro

Re: Circles

Thanks alot!

4. Sep 30, 2010

### Mentallic

Re: Circles

No problem You don't even have to consider which quadrants the line is in, just start solving for that line and the lines y=x and y=-x.

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