What does trigonometry study?

Trigonometry primarily focuses on the relationships between the angles and sides of triangles. This area of mathematics is essential for calculating unknown lengths and angles, particularly in right-angled triangles, where definitions of functions such as sine, cosine, and tangent are established.

While it is correct to acknowledge that trigonometry also relates to angles and has applications involving circular concepts—such as sine and cosine waves which can be associated with circular motion—the core definition and study of trigonometry are most closely aligned with triangle measurements. Therefore, the emphasis on triangle measurement makes it the most fitting choice in this context.

Understanding that all three elements mentioned in the options are interconnected is helpful, but the specific focus of trigonometry remains squarely on the properties and relations of triangles.