01
How to use this calculator
- Enter the known endpoint and the midpoint.
- Double each midpoint coordinate.
- Subtract the corresponding known endpoint coordinate.
02
A little understanding goes a long way.
The missing endpoint formula rearranges the midpoint equation. It reflects the known endpoint through the midpoint.
THE FORMULA
B = (2mₓ − aₓ, 2mᵧ − aᵧ)
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A worked example
With endpoint A = (2, 4) and midpoint M = (5, 7), the other endpoint is B = (10 − 2, 14 − 4) = (8, 10).
03
A few common questions
How can I check the result?
Average the two endpoint coordinates. The result should reproduce the given midpoint.
Can the result be negative?
Yes. A negative coordinate simply locates the point on the opposite side of an axis.