Give the Cartesian sign convention for measuring distances in spherical mirrors and lenses.

Explanation

(1) The distances measured in the same direction as the incident light are taken as positive and those measured in the direction opposite to the direction of the incident light are taken as negative.
(2) The heights measured upwards with respect to the X -axis and normal to the principal axis of the mirror/lens are taken as positive and heights measured downwards below the axis are taken as negative.