This is called difference quotient. The formula_22 now gets closer to formula_23. This can be expressed with the following formula:
ð ɪ s WORD_BOUNDARY ɪ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY d ɪ f ɹ ə n s WORD_BOUNDARY k w oʊ ʃ ə n t WORD_BOUNDARY ð ə WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY t w ɛ n t i WORD_BOUNDARY t uː WORD_BOUNDARY n aʊ WORD_BOUNDARY ɡ ɛ t s WORD_BOUNDARY k l oʊ s ə ɹ WORD_BOUNDARY t ə WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY t w ɛ n t i WORD_BOUNDARY θ ɹ iː WORD_BOUNDARY ð ɪ s WORD_BOUNDARY k æ n WORD_BOUNDARY b iː WORD_BOUNDARY ɛ k s p ɹ ɛ s t WORD_BOUNDARY w ɪ ð ð ə WORD_BOUNDARY f ɑ l oʊ ɪ ŋ WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY