formula_1 is defined as the ratio of a circle's circumference formula_4 to its diameter formula_5:
f ɔ ɹ m j ʊ l ə WORD_BOUNDARY w ʌ n WORD_BOUNDARY ɪ z WORD_BOUNDARY d ɪ f aɪ n d WORD_BOUNDARY æ z WORD_BOUNDARY ð ə WORD_BOUNDARY ɹ eɪ ʃ ɪ oʊ WORD_BOUNDARY ə v ə WORD_BOUNDARY s ɜː k ə l z WORD_BOUNDARY s ɜː k ʌ m f ɹ ə n s WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY f ɔ ɹ WORD_BOUNDARY t ʊ WORD_BOUNDARY ɪ t s WORD_BOUNDARY d aɪ æ m ɪ t ə ɹ WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY f aɪ v WORD_BOUNDARY