Question

using Cartesian sign conventions, derive the mirror formula
of concave mirror when real image is formed?
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Answer 1

Sign is taken as + (positive) behind the spherical mirror. For example if an image is formed behind the mirror, the distance of image is taken as + (positive) from pole along the principal axis. The height of is taken as + (positive) above the principal axis and taken as – (negative) below the principal axis.