When formula_4, the function is called a Maclaurin series. The Maclaurin series written as a power series looks like:
w ɛ n WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY f ɔ ɹ WORD_BOUNDARY ð ə WORD_BOUNDARY f ʌ ŋ k ʃ ə n WORD_BOUNDARY ɪ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY ʌ WORD_BOUNDARY m ə k l ɔ ɹ ɪ n WORD_BOUNDARY s ɪ ɹ i z WORD_BOUNDARY ð ə WORD_BOUNDARY m ə k l ɔ ɹ ɪ n WORD_BOUNDARY s ɪ ɹ i z WORD_BOUNDARY ɹ ɪ t ə n WORD_BOUNDARY æ z WORD_BOUNDARY ʌ WORD_BOUNDARY p aʊ ə ɹ WORD_BOUNDARY s ɪ ɹ i z WORD_BOUNDARY l ʊ k s WORD_BOUNDARY l aɪ k WORD_BOUNDARY