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Jan 21 at 0:26 comment added JoshuaZ @KevinBuzzard , Possibly if one is continuing in the same direction, maybe going with Brahmagupta's formula's next would make sense.
Aug 8, 2019 at 12:15 comment added Andrea Ferretti Another easy one is Apollonius theorem: let ABC be a triangle right in A. The midpoints of the three sides and the foot of the altitude drawn from A to BC all lie on one circle. But again, it may be too easy...
Aug 7, 2019 at 18:03 comment added Kevin Buzzard We need a better toy example.
Aug 7, 2019 at 12:51 comment added user44143 For what it’s worth, this can also be done easily enough by hand. We have $2ax=a^2+b^2-c^2$, so $(2ab)^2=(2ax)^2+(2ay)^2=(a^2+b^2-c^2)^2+16s^2$, and the result follows by rearranging and factoring the differences of squares.
Aug 7, 2019 at 12:26 comment added François Brunault I regularly ask the students to prove Héron's formula with Sage and it works well, resultants are sufficient.
Aug 7, 2019 at 12:26 comment added Andrea Ferretti @KevinBuzzard done, see my edit - in fact it was quicker and easier than I thought
Aug 7, 2019 at 12:26 history edited Andrea Ferretti CC BY-SA 4.0
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Aug 7, 2019 at 12:17 history edited Andrea Ferretti CC BY-SA 4.0
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Aug 7, 2019 at 12:06 comment added Andrea Ferretti It is a classic example, so I did not perform the computation myself, but I may try later using github.com/PoslavskySV/rings . I will let you know how long it takes
Aug 7, 2019 at 11:34 comment added Kevin Buzzard I have a gut feeling that some olympiad problems will not be solvable in this way because they might involve assertions about only some roots. (a+b-c)(c+a-b)(b+c-a)(a+b+c) is a polynomial function of a^2, b^2 and c^2, so issues of sign do not show up. What about an analogous question where it's essential that b is chosen to be the positive square root, and where the claimed equation does not hold if the negative one is chosen? I think that's why Groebner bases are not sufficient here but I do not know a good toy example.
Aug 7, 2019 at 11:30 comment added Kevin Buzzard Did you do these calculations? Using which system? How long did they take?
Aug 7, 2019 at 10:59 comment added Turbo Looks like there should be lot more identities.
Aug 7, 2019 at 9:01 history answered Andrea Ferretti CC BY-SA 4.0