Moreover, in 1637, René Descartes "invented the convention of representing unknowns in equations by x, y, and z, and knowns by a, b, and c", and this convention is still often followed, especially in elementary algebra.
moːɹˈoʊvɚ, ɪn wˈʌn θˈaʊzənd sˈɪkshˈʌndɹɪd θˈɜːɾi sˈɛvən, ɹᵻnˈeɪ dᵻskˈɑːɹts "ɪnvˈɛntᵻd ðə kənvˈɛnʃən ʌv ɹˌɛpɹᵻzˈɛntɪŋ ʌnnˈoʊnz ɪn ᵻkwˈeɪʒənz baɪ ˈɛks, wˈaɪ, ænd zˈiː, ænd nˈoʊnz baɪ ˈeɪ, bˈiː, ænd sˈiː", ænd ðɪs kənvˈɛnʃən ɪz stˈɪl ˈɔfən fˈɑːloʊd, ɪspˈɛʃəli ɪn ˌɛlɪmˈɛntɚɹi ˈældʒᵻbɹə.