私的メモ:
https://ja.wolframalpha.com/input?i=FindFit%5B%7B%281%2C+3%29%2C+%282%2C+9%29%2C+%283%2C+19%29%7D%2C+ab%5Ex%2Bc%2C+%7Ba%2C+b%2C+c%7D%2C+x%5D
https://ja.wolframalpha.com/input?i=NonlinearModelFit%5B%7B%281%2C+3%29%2C+%282%2C+9%29%2C+%283%2C+19%29%7D%2C+ab%5Ex%2Bc%2C+%7Ba%2C+b%2C+c%7D%2C+x%5D
指数関数の方はこれらとほぼ同じだが、これらだと厳密解として出ないので気に食わない
https://ja.wolframalpha.com/input?i=Solve%5BCircleThrough%5B%281%2C+3%29%2C+%282%2C+9%29%2C+%283%2C+19%29%5D%2C+y%5D
円の方はこれでは実行すらされず、他に厳密解を出せそうな方法も発見できず、泣きながら敗退