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Charles Gilman wrote on Mon, Feb 14, 2011 06:49 AM UTC:
```Actually you don't need to take my word for it about root 7, just the word of whichever mathematician it was - I cannot remember offhand - who extrapolated Pythagoras' theorem to
aÂ²+bÂ²-2ab cosine(internal angle between a and b)=cÂ²
for any sides of any triangle. For an internal angle of 180Â° - straight on - this renders cÂ² as aÂ²+bÂ²+2ab which many will recognise as indeed the formula for (a+b)Â². Likewise for 0Â° - doubling back - it gives aÂ²+bÂ²-2ab which many will recognise as the formula for (a-b)Â². For 90Â° it gives Pythagoras' original aÂ²+bÂ². For 120Â° it gives aÂ²+bÂ²+ab. In the case of the Sennight this is 2Â²+1Â²+(2x1)=7.```

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