Write the sign conventions for spherical mirrors.

Explanation

### Step-by-Step Solution:

1. **Definition of Pole**:
- The pole of the spherical mirror is the central point on the mirror's surface. All distances are measured from this point.
- **Sign Convention**: All distances are measured from the pole of the mirror.

2. **Direction of Light**:
- When light travels towards the mirror, the distance in the direction of light is considered positive.
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