According to the thin lens formula, which one of the following is true regarding the focal length of the lens?

Thin lens formula is given as:1f=1v-1uWhere u = distance of the object from the optical center of the lens; v = distance of the image from the optical center of the lens; f = focal length of a lens. According to the thin lens formula, f is positive for converging or convex lens and f is negative for a diverging or concave lens.