Это вот формулировка утверждения о разложении в ряд для синуса и косинуса (точнее,

) из трактата
Юктибхаша, датирующегося примерно 1530 годом. Доказательство там вроде тоже есть ранее по тексту, хотя я не вникал.
Цитата:
Thus, since the results were (actually) obtained from the sum of the arcs, while it was required to obtain them from the sum of Rsines, the correction terms are all in excess of the actual results. Therefore, the successive correction terms (saṃskāra-phala) at every higher stage should be subtracted from the earlier correction-results. This being the case, the following is the procedure (kriyā-krama) to be adopted. The required arc is the first result. When this is squared, halved and divided by the radius, the second result is got. Keep this second result separately. Now multiply the second result also by the arc and divide by 3 and also by radius. Place the result got below the first result. Then multiply this also by the arc and divide by four and the radius. Keep the result below the second result. In this manner, derive successive results by multiplying the previous result by the arc, and dividing by corresponding successive numbers 1, 2, 3 etc. and by radius. Now, place below the first result the odd results, viz., the third, the fifth etc., and place below the second result the even results, viz., the fourth, sixth etc. Then subtract successively the bottom result from the one above it, the remainder from the one still above it. Ultimately, in the first column (paṅkti), the resultant first result will be left and in the second column the resultant second result will be left. These will be the required Rsine and Rversine.
Цитирую по
изданию 2008 года, § 7.5.5. Это перевод с языка малаялам (там есть и оригинальный текст).