How to get circumcircle midpoint and radius in Lua?

I've tried to make a function in Lua to get the circumcircle, circumcenter and radius, but something goes wrong:

local function getCircumcircle (x1, y1, x2, y2, x3, y3)
    local d = 2*(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))
    local t1, t2, t3 = x1*x1+y1*y1, x2*x2+y2*y2, x3*x3+y3*y3
    local x = (t1*(y2-y3)+t2*(y3-y1)+t3*(y1-y2))/d
    local y = (t1*(x3-x2)+t2*(x1-x3)+t3*(x2-x1))/d
    local radius = math.sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y))
end

Thanks, Ivo, my bad.

local function getCircumcircle (x1, y1, x2, y2, x3, y3)
    local d = 2*(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))
    local t1, t2, t3 = x1*x1+y1*y1, x2*x2+y2*y2, x3*x3+y3*y3
    local cx = (t1*(y2-y3)+t2*(y3-y1)+t3*(y1-y2))/d
    local cy = (t1*(x3-x2)+t2*(x1-x3)+t3*(x2-x1))/d
    local radius = math.sqrt((x1-cx)*(x1-cx)+(y1-cy)*(y1-cy))
    return cx,cy,radius
end

Updated, new version with points:

-- calculates circumcircle for three points
local function getCircumcircle(p1, p2, p3)
    local x1, y1 = p1.x, p1.y
    local x2, y2 = p2.x, p2.y
    local x3, y3 = p3.x, p3.y

    -- calculate denominator
    local d = 2 * (x1*(y2-y3) + x2*(y3-y1) + x3*(y1-y2))
    if math.abs(d) < 0.0001 then  -- points are collinear
        return nil
    end

    -- calculate center coordinates
    local t1 = x1*x1 + y1*y1
    local t2 = x2*x2 + y2*y2
    local t3 = x3*x3 + y3*y3

    local cx = (t1*(y2-y3) + t2*(y3-y1) + t3*(y1-y2)) / d
    local cy = (t1*(x3-x2) + t2*(x1-x3) + t3*(x2-x1)) / d

    -- calculate radius
    local radius = math.sqrt((x1-cx)^2 + (y1-cy)^2)

    return {
        x = cx,
        y = cy,
        radius = radius
    }
end