Wednesday, January 21, 2015

pronunciation - What do I call the ′ in mathematical formulae?


As in x′ = x + t


"Ex (?) equals ex plus tee".



In Russian it is called "штрих" (shtrikch).



Answer



The single tick following a variable is often (but not always) used to represent a derivative and (in the United States) is always pronounced "prime." In your example, "Ex prime = ex plus tee."


f(x) = x² <--- "Eff of ex equals ex squared."


f′(x) = 2 x <---- "Eff prime of ex equals two ex."


f′′(x) = 2 <---- "Eff double prime of ex equals two."


In non-mathematical contexts it is called a single quote (or a "tick"). This wikipedia entry differentiates between the prime symbol and the single quote. As they also note, using a single quote (') as a stand-in for prime (′) is not uncommon. Thanks Vi for the link.


I have learned from other respondents that in the UK, Canada and Australia, it is pronounced prime unless it signals a derivative, in which case it can be pronounced dash.




In case you run into these two:



is pronounced "ex bar"


is pronounced "ex hat"


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