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Parallel Triangle Segment Ratios and Missing Length

No. DB is the remaining part from D to B, and EC is the remaining part from E to C. The full sides are AD+DB and AE+EC.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Example in initial displayed units: AD 2, DB 3, AE 4 gives EC 6.

AD/DB = AE/EC

Worked example

Enter these known values and leave the other values blank.

AD
2 cm
DB
3 cm
AE
4 cm
EC
6 cm

Assumptions and limitations

  • D lies on side AB and E lies on side AC, with DE parallel to BC. The four positive lengths are portions of those sides, not the entire side lengths. Three compatible segment measures determine the fourth. The ratio alone does not establish that a proposed line is parallel in a measured drawing.
  • Clear unknown measurements before solving backward. Use compatible units and independent values. Reference pictures are original schematic drawings. Independently rounded measurements can fail strict compatibility at a boundary.

Common questions

Are DB and EC the full triangle sides?

No. DB is the remaining part from D to B, and EC is the remaining part from E to C. The full sides are AD+DB and AE+EC.

How do I use this calculator with different units?

Select the unit beside each measure. Length, squared length and volume use different dimensions; changing a unit preserves the physical value. Compound length controls represent feet/inches or meters/centimeters together.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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