src/Maths/Geometry/Circle.php
public function getAbscissaByOrdinate($y)
    {
        $o = $this->getPointO();
        return (sqrt(pow($this->getRadius(), 2) - pow(($y - $o->getOrdinate()), 2)) + $o->getAbscissa());
    }
public function getAbscissaByOrdinate($y)
    {
        $o = $this->getPointO();
        return (sqrt(pow($this->getRadius(), 2) - pow(($y - $o->getOrdinate()), 2)) + $o->getAbscissa());
    }
Get the abscissa of a point of the circle by its ordinate

x = sqrt( r^2 - (y - Oy)^2 ) + Ox

@param   float   $y
@return  float