In mathematical analysis, delta x is introduced when defining derivative, which is expressed as the change (increment) of independent variable;

Second, read △

△ appears in the Greek alphabet. δ (uppercase), δ (lowercase), and the sound name δ? λ τ α, the Greek letter name is/? Eelta/, American English is delta (International Phonetic Alphabet /'d ε lt? /)。 So δx is pronounced δ X.