# Simplifying an equation (circle)

I'm trying to work on a problem, and I'm stuck at simplifying this equation. I do not why I cannot see it:

so the book gives the following equation:

$$\frac{ax}{x^2+y^2}+\frac{by}{x^2+y^2}+c=0$$

where c is nonzero.

Now the book simplifies it like this:

$$x^2+y^2+\frac{a}{c} x+\frac{b}{c} y=0$$

Does anyone know how they simplified it? I believe they divided c, but I do not know how $x^2+y^2$ disappeared

Also, this involves the equation of a circle

Hint: multiply both sides by $x^2 + y^2$ to clear the fractions, then simplify.