-- Input variables
local angle = math.PI/3 -- 60 degrees, arbitrarily chosen
local x, y = 12, 53 -- Cursor offsets, arbitrarily chosen

-- Algorithm
local u, v = math.cos(angle), math.sin(angle)
local dp = (x*u + y*v) -- Vector dot product
local projX, projY = dp*x, dp*y

-- The radius is the length of the vector, or sqrt(x^2 + y^2)
local radius = sqrt(projX^2 + projY^2);

return radius;