Where does “مثلثات” come from?

مثلثات (Persian) comes from Arabic مُثَلَّثَات.

مثلثات (Persian): plural of مثلث; trigonometry

Definitions

Step	Language	Word	Meaning
1	Arabic	مُثَلَّثَات	—

مثلثات — Etymology, Origin & Word History | Etymology Explorer