Surya Siddhanta
ग्राह्यग्राहकसम्योगवियोगौ दलितौ पृथक् । विक्षेपवर्गहीनाभ्याम् तद्वर्गाभ्याम् उभे पदे॥
Find the halves separately of the sum and difference of the diameter of that which is to be covered and that which is the coverer. Subtract the square of the (Moon's) latitude (as found at the time of the syzygy) severally from the squares of the half sum and the half difference and take the square-roots of the results.
english translation
grAhyagrAhakasamyogaviyogau dalitau pRthak । vikSepavargahInAbhyAm tadvargAbhyAm ubhe pade॥
hk transliteration by Sanscript