For example, formula_4 because formula_5. The 8 in that example is called the radicand, the 3 is called the index, and the check-shaped part is called the radical symbol or radical sign.
f ɔ ɹ WORD_BOUNDARY ɛ ɡ z æ m p ə l WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY f ɔ ɹ WORD_BOUNDARY b ɪ k ʌ z WORD_BOUNDARY f ɔ ɹ m j ʊ l ə WORD_BOUNDARY f aɪ v WORD_BOUNDARY ð ɪ WORD_BOUNDARY eɪ t WORD_BOUNDARY ɪ n WORD_BOUNDARY ð æ t WORD_BOUNDARY ɛ ɡ z æ m p ə l WORD_BOUNDARY ɪ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY ð ə WORD_BOUNDARY ɹ æ d ɪ k æ n d WORD_BOUNDARY ð ə WORD_BOUNDARY θ ɹ iː WORD_BOUNDARY ɪ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY ð ɪ WORD_BOUNDARY ɪ n d ɛ k s WORD_BOUNDARY æ n d WORD_BOUNDARY ð ə WORD_BOUNDARY t̠ʃ ɛ k ʃ eɪ p t WORD_BOUNDARY p ɑ ɹ t WORD_BOUNDARY ɪ z WORD_BOUNDARY k ɔ l d WORD_BOUNDARY ð ə WORD_BOUNDARY ɹ æ d ɪ k ə l WORD_BOUNDARY s ɪ m b ə l WORD_BOUNDARY ɔ ɹ WORD_BOUNDARY ɹ æ d ɪ k ə l WORD_BOUNDARY s aɪ n WORD_BOUNDARY