The phrase "ambiguous formulae" is correct and usable in written English.
It can be used when discussing mathematical or logical expressions that can be interpreted in multiple ways.
Example: "The ambiguous formulae in the report led to confusion among the researchers regarding the results."
Alternatives: "unclear formulas" or "vague expressions".
In the various colloquies between Protestants and Catholics or between German Lutheran and Swiss Reform churchmen, Bucer often advocated the use of obscure language and ambiguous formulas when explicit agreement between the opposing parties was impossible to attain.
Charters were granted to groups of nobles in almost every province of France. Louis bought the support of the clergy by similar means; but whereas they gained for the church some real privileges, the use of ambiguous formulas made the baronial charters virtually worthless.
This new and ambiguous formula fanned the flames of controversy, as subordinationists and anti-subordinationists understood the phrase differently when signing on to it, and later argued for conflicting interpretations of it.
To the extent that judges would seek to faithfully adhere to its ambiguous formula--not too broad, not too deep--they are left with little guidance about how or even when to do so.
Modern-day Democrats are constitutionally incapable of sharp and bold; Nancy Pelosi's op-ed announcing the Better Deal in the Washington Post, for example, is swimming in the same sort of ambiguous futurific formulas that Americans are wary of but that Democrats seem to love.
Activist shareholders have been criticizing executive pay practices for well over a decade, accusing directors of being too cozy with C.E.O.'s, too eager to lavish pay on them and too ambiguous about the formulas they use for setting compensation.
The ambiguous use of formula prayers (common among the Ṣūfīs) such as Allāhu akbar, "God is most great," or perhaps "God is Akbar," hinted at a divine association as well.
Also, when the animated pedagogical agents speak there are challenges with articulating the sometimes ambiguous syntax of formulas.
And this seems right, because commonly the linguistic meaning of a formula is ambiguous (in terms of background linguistic possibilities), and in order to identify the relevant meaning one must turn, not only (as already mentioned) to larger bodies of text, but also to hypotheses, largely derived therefrom, concerning the author's intentions (e.g. concerning the subject-matter he intends to treat).
Identifying the molecular formula of a compound is already a challenging problem: most peaks in an LC MS run are ambiguous and can be explained by several molecular formulas, even when using instruments with high mass accuracy.
