Trigonometry is a branch of mathematics that deals with the relationships between the sides and angles of triangles. It is used extensively in fields such as engineering, physics, and astronomy.

The three primary trigonometric functions are sine, cosine, and tangent. These functions relate the ratios of the sides of a right triangle to the angles opposite them. The sine function relates the ratio of the opposite side to the hypotenuse, the cosine function relates the ratio of the adjacent side to the hypotenuse, and the tangent function relates the ratio of the opposite side to the adjacent side.

Trigonometry also includes other functions such as secant, cosecant, and cotangent, which are reciprocals of the primary functions. Additionally, trigonometric identities and equations are used to solve problems involving angles and sides of triangles.

Trigonometry has many practical applications, such as in navigation, surveying, and construction. It is also used in fields such as music and art, where it is used to create and analyze patterns and shapes.