In uniform circular motion, centripetal acceleration a_c = v²/r. However, in tangential and radial acceleration, radial acceleration a_r = - a_c = - v²/r. Why a_c do not have a negative while a_r do have a negative sign? I know radius vector starts at origin and point outward, but I thought centripetal acceleration and radial acceleration should both have a negative sign since they both point to the origin