Rewrite a circle's equation to easily see centre and radius $$x^{2}+y^{2}-5x-15y+30=0$$
I'm supposed to rewrite this equation so that you can easily see the centre and radius of the circle. I don't even know where to start. According to Mathematica the centre is $(5/2, 15/2)$ and the radius is $\sqrt{65/2}$.

Answer:
$$x^2 +y^2 -5x-15y+30 = 0$$
$$x^2 -5x +(\frac{5}{2})^2 +y^2 -15x +(\frac{15}{2})^2 -(\frac{5}{2})^2-(\frac{15}{2})^2+30 = 0$$
$$(x-\frac{5}{2})^2+(y-\frac{15}{2})^2 = \frac{225+25}{4}-30$$
$$(x-\frac{5}{2})^2+(y-\frac{15}{2})^2 =(\sqrt{\frac{65}{2}})^2$$
Center$$ (\frac{5}{2},\frac{15}{2})$$and the radius $$= \sqrt{\frac{65}{2}}$$
