1 Chills and Tingling fingers and Skin symptoms (4 causes) 2  Chills and Tingling fingers and Temperature symptoms (4 causes) 3  Chills and Tingling fingers and Body symptoms (3 causes) 4  Chills and Tingling fingers and Leg symptoms (3 causes)  Chills and Tingling fingers and Limb symptoms (3 causes)
From the geometry of the spherical mirror, note that the focal length is half the radius of curvature: As in the case of lenses, the cartesian sign convention is used here, and that is the origin of the negative sign above. The radius r for a concave mirror is a negative quantity (going left from the surface), and this gives a positive focal length, implying convergence.
When parallel rays of light pass through a concave lens the refracted rays diverge so that they appear to come from one point called the principal focus. The distance between the principal focus and the centre of the lens is called the focal length. The image formed is virtual and diminished (smaller).