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

111 δ (Sin x) = Cos x δx. Since H Sin (x+1)° = H Sin x + (H Cos x × H Sin 1°) / R approximately, H Sin (x + 1)° — H Sin x° = H Cos x × (H Sin 1° / R) = H Cos x × a constant. Hence Bhāskara could see that the variation in the function H Sin x is proportional to H Cos x. Let it be now required to find the increment in H Sin x for an increment δx in x where δx < 60'. Let H Sin (x+1)° — H Sin x = (60' × H Cos x) / R = y where y is called the Bhogya-Khanda. Then Bhāskara argues “If for an increment of 60', there is an increment of y, what shall we have for δx ?”. The answer is yδx / 60 = (60 × H Cos x / R) × (δx / 60) = (H Cos x × δx) / R. Hence H Sin (x + δx) — H Sin x = δ