Missing Endpoint Calculator
Know one endpoint and the midpoint? This page finds the other endpoint with B = 2M − A. It handles 2D and 3D coordinates, keeps fractions exact, and shows the substitution beside a schematic projection. For A = (1, 2, 3) and M = (3, 4, 5), the missing endpoint is (5, 6, 7).
Use integers, decimals or fractions such as −4, 0.25 or 1/3. Type a standard minus sign (-) for negatives. Up to 100 digits per coordinate.
Decimal preview: (5, 6, 7)
- x = 2 × (3) − (1) = 5
- y = 2 × (4) − (2) = 6
- z = 2 × (5) − (3) = 7
A (1, 2, 3) · M (3, 4, 5) · B (5, 6, 7). Coincident or very close coordinates may overlap in this projection; the exact values above remain authoritative.
Batch worksheet
Up to 200 segments. One row per segment, with an ID followed by 6 coordinates separated by commas or tabs. Uses the mode and dimensions selected above. IDs stay attached to results and errors.
| ID | Exact result | Working / error |
|---|---|---|
| segment-1 | Check input | Expected ID followed by 6 coordinates, separated by commas or tabs. |
| segment-2 | Check input | Expected ID followed by 6 coordinates, separated by commas or tabs. |
Coordinates use exact rational arithmetic. Decimal previews are rounded to 12 places; the diagram is schematic and uses the selected axes. These are Cartesian coordinates, not geographic distances. Coordinates are processed on this device and are not saved automatically.
Common questions
- How do you find a missing endpoint from a midpoint?
- Double each midpoint coordinate and subtract the matching coordinate of the known endpoint: B = 2M − A.
- Can I use fractions and 3D points?
- Yes. Coordinates can be integers, decimals or fractions up to 100 digits, and the 3D mode calculates x, y and z independently.
Coordinates use exact rational arithmetic. Decimal previews are rounded to 12 places; the diagram is schematic and uses the selected axes. These are Cartesian coordinates, not geographic distances.