Free · Coordinate geometry
Segment Length and Collinearity Calculator
Add or subtract segment lengths and identify which point lies between the other two from exact distances.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
Segments AB = 3 and BC = 4 give AC = 7 when B lies between A and C.
AC = AB + BC; collinear distances have one length equal to the sum of the other two.
Worked example
Enter these known values and leave the other values blank.
- AB
- 3 cm
- BC
- 4 cm
- AC
- 7 cm
Assumptions and limitations
- In length mode, B lies strictly between A and C; AC = AB + BC and all segment lengths must be positive.
- The collinearity mode checks exact distance equalities in each possible point order. Rounded measurements may not satisfy exact equality. A failed equality alone does not prove the entered lengths describe a possible triangle.
- All lengths share a common unit basis. Clear the unknown before solving an inverse; locks retain entered values.
Common questions
How do I find a missing segment?
When B lies between A and C, add AB and BC to find AC, or subtract either smaller segment from AC.
Can I use rounded measurements to prove collinearity?
The collinearity mode checks exact distance equalities in each possible point order. Rounded measurements may not satisfy exact equality. A failed equality alone does not prove the entered lengths describe a possible triangle.
References
Replace four external segment pictures with original accessible point-order layouts and exact segment identities, retaining every mode and image condition. Use exact sign-of-residual equality for each possible middle point; tolerant relational comparisons must not certify an unequal sum as collinear. Enforce exact strict positive segment lengths without a tolerance-based lower length bound.