二次方程式

Nov 17 2016
def quadraticFormula := qF

def qF f x :=
  match coefficients f x as list mathExpr with
    | [$a_0, $a_1, $a_2] -> qF' a_2 a_1 a_0

def qF' a b c :=
  match (a, b, c) as (mathExpr, mathExpr, mathExpr) with
    | (#1, #0, _) -> (sqrt (- c), - sqrt (- c))
    | (#1, _, _) ->
      (2)#((- (b / 2)) + %1, (- (b / 2)) + %2)
        (withSymbols [x, y]
          qF (substitute [(x, y - b / 2)] (x ^ 2 + b * x + c)) y)
    | (_, _, _) -> qF' 1 (b / a) (c / a)

qF (x ^ 2 + x + 1) x
-- ((-1 + i * sqrt 3) / 2, (-1 - i * sqrt 3) / 2)

qF (x ^ 2 + b * x + c) x
-- ((- b + sqrt (b^2 - 4 * c)) / 2, (- b - sqrt (b^2 - 4 * c)) / 2)

qF (a * x ^ 2 + b * x + c) x
-- ((- b + sqrt (b^2 - 4 * a * c)) / (2 * a), (- b - sqrt (b^2 - 4 * a * c)) / (2 * a))

qF (a * x ^ 2 + 2 * b * x + c) x
-- ((- b + sqrt (b^2 - a * c)) / a, (- b - sqrt (b^2 - a * c)) / a)
リンク

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