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

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Fig. 56
and add Chara to Unnata when δ < 0 and take the H sine
of the result. Let us first consider the case when δ > 0.
(Refer fig. 56) when the Sun is at ☉, Iṣṭa Śaṅku is H sin ☉L;
and Unmandala Śaṅku is H sin BM. When the
Sun is at ☉₁, Iṣṭa Śaṅku = H sin ☉₁N. In the first case
Iṣṭayaṣṭi = (H sin ☉L — H sin BM) which will be the
orthogonal projection of ☉B on the meridian plane.
Unmandala Śaṅku and the Iṣṭa Śaṅku in the position ☉₁
are similarly the orthogonal projections of BM and ☉₁N
on the same plane. In the position ☉ Iṣṭa Śaṅku =
Unmandala Śaṅku + Iṣṭayaṣṭi, whereas in the position
☉₁, Iṣṭa Śaṅku = Unmandala Śaṅku — Iṣṭayaṣṭi which is
now downwards. Thus in the place of addition we have
subtraction of Iṣṭayaṣṭi. This reversion has arisen out of
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