सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

280 the rising hour angle and ℎ = L P̂ Q and Chara by the arc EM and Sūtra = H sin (MN + EM) = H sin (unnata + chara) = H sin EN = H sin (90 - ℎ) = H cos ℎ. Verse 55. Sūtra multiplied by Kujyā and divided by Charajyā will be also Kalā and Kalā multiplied by the Koti and divided by the Karṇa of any latitudinal triangle will be Iṣṭa yaṣṭi. Comm. In as much as Kalā is the corresponding line in the diurnal circle to the Sūtra in the plane of the celestial equator Sūtra / Kalā = R / (H cos δ) = Charajyā / Kujyā ∴ (Sūtra × Kujyā) / Charajyā = Kalā In verse 33, we saw that Dinārdha Sanku — Unmandala Sanku = Yaṣṭi. This Iṣṭa-yaṣṭi will be therefore the perpendicular dropped from 𝑛, the Sun's position in the diurnal circle on the plane parallel to the horizon and passing through the head of the Unmandala Sanku ie. passing through B and parallel to the horizon in fig. 21. Since the angle between the diurnal plane and the vertical plane of the yaṣṭi is equal to φ the latitude, the Iṣṭayaṣṭi forms a latitudinal triangle with the Kalā, it being the Koti or side opposite to the angle 90 - φ and the Kalā being the hypotenuse, ∴ Yaṣṭi / Kalā = cos φ = Koti of a latitudinal triangle / Karṇa of a latitudinal triangle ∴ Iṣṭayaṣṭi = Kalā × (Koti of a latitudinal triangle) / Karṇa When the Sun is on the meridian, Iṣṭayaṣṭi becomes yaṣṭi of verse 33. The formula for Iṣṭayaṣṭi is therefore (Kalā × H cos φ) / R = (H cos δ · H cos ℎ) / R × (H cos φ) / R from formula (27) = (H cos φ · H cos δ · H cos ℎ) / R² 27'