Chapter 3 of NCERT 11th maths is about Trigonometric Functions. Trigonometry is a branch of mathematics that deals with the relationships between the sides and angles of triangles. In this chapter, you will learn about the six trigonometric functions: sine, cosine, tangent, cosecant, secant, and cotangent. You will also learn about the unit circle, which is a circle with a radius of one unit, and how it is used to find the values of trigonometric functions. Additionally, you will learn about the properties of trigonometric functions, such as periodicity, evenness, and oddness. This chapter is important for understanding calculus and other advanced topics in mathematics.