Lagrange's notation apostrophe prime function derivative
In Lagrange's notation, the symbol for a derivative is an apostrophe-like mark called a prime. Thus, the derivative of a function called f is denoted by f′, pronounced "f prime" or "f dash". For instance, if f(x) = x is the squaring function, then f′(x) = 2x is its derivative (the doubling function g from above).
