1. Jan 15, 2006

### m00c0w

I'm trying to calculate the radius of the circle $$x^2 - 2ax + y^2 - 2ay = 0$$
I completed the square and got to $$(x-a)^2 + (y-a)^2 = 2{a}^2$$
That would mean the radius is $$\sqrt{2{a}^2}$$ right? Which would be $$\sqrt{2}\sqrt{a^2} \Rightarrow a\sqrt{2}$$... but my textbook quotes the answer as $$\sqrt{2a}$$ Did I do something wrong or is my textbook incorrect?

2. Jan 15, 2006

### arildno

Are you sure you are reading your textbook? It might be that the answer is $\sqrt{2}a[/tex] but a little blurred so it is not clear where the square root sign ends- it looks like [itex]\sqrt{2a}$.
On the otherhand that is exactly why most texts would use the clearer $a\sqrt{2}$ as you do.