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In the Cartesian sign convention used in ray optics:
AAll distances are measured from the centre of curvature
BAll distances are measured from the pole/optical centre; distances in the direction of incident light are positive, opposite to it are negative; heights above the principal axis are positive
CAll distances are positive
DHeights below the axis are positive
Answer & Solution
Correct answer: B. All distances are measured from the pole/optical centre; distances in the direction of incident light are positive, opposite to it are negative; heights above the principal axis are positive
**Cartesian sign convention**: origin = pole (mirror) or optical centre (lens). Incident light travels along +x direction → distances *along* incident light are **+**, *against* incident light are **−**. Heights above principal axis are **+**, below are **−**. With this convention, one formula handles all cases.
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