Brihat Parashara Hora Shastra
क्रमादुत्क्रमतो ग्राह्यं त्रिकोणं विषमे समे । त्रिकोणाख्यदशा प्रोक्ता समा नाथावसानकाः ॥ १८४॥
Here also the Dashas of the Rāśis will be in the onwards order in the case of odd Rāśis and in the reverse order in the case of even Rāśis. The Dasha years will be similar to that of Char Dasha. It has been named Trikon because of the commencement of the Dasha from the Rāśis in Konas.
english translation
kramAdutkramato grAhyaM trikoNaM viSame same । trikoNAkhyadazA proktA samA nAthAvasAnakAH ॥ 184॥
hk transliteration by Sanscript