trigonometry
branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides
en-US/ˌtɹiɡəˈnɑmɪtɹi/
en-GB/ˌtɹɪɡəˈnɒmətɹɪ/
branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides