👉 In mathematics, a "derat" is a mathematical function that is not defined at some points. In other words, it's undefined at those values of the independent variable where its derivative does not exist. For example: 1. The function f(x) = x^2 - 4x + 3 (where x ≠ 0) 2. The function g(x) = |x| (where x ≠ 0) These functions are considered "derats" because they do not