Trigonometry is the branch of mathematics dealing with the relationships between angles and sides of triangles.
Trigonometry studies the six trigonometric functions: sin, cos, tan, csc, sec, and cot. These functions relate angles to side ratios in right triangles. Trigonometric functions are periodic and describe oscillations, waves, and circular motion. Applications include navigation, astronomy, engineering, physics, and computer graphics.
Trigonometry began with Greek astronomers like Hipparchus (150 BCE). Indian mathematicians developed sine and cosine. Islamic scholars like Al-Battani advanced the field. Euler unified trigonometry with complex numbers.