Chapter 3 of the NCERT 11th maths book focuses on Trigonometric Functions. The main ideas from this chapter are:

1. Trigonometric ratios: The chapter starts with the definition of trigonometric ratios such as sine, cosine, and tangent. These ratios are used to find the angles and sides of a right-angled triangle.

2. Trigonometric identities: The chapter explains various trigonometric identities such as Pythagorean identities, reciprocal identities, quotient identities, and co-function identities. These identities are used to simplify trigonometric expressions.

3. Trigonometric functions: The chapter defines trigonometric functions such as sine, cosine, tangent, cosecant, secant, and cotangent. These functions are used to find the values of angles and sides of a triangle.

4. Inverse trigonometric functions: The chapter explains the concept of inverse trigonometric functions such as arcsine, arccosine, and arctangent. These functions are used to find the angle whose trigonometric ratio is given.

5. Trigonometric equations: The chapter explains how to solve trigonometric equations using various trigonometric identities and formulas.

Overall, this chapter is important for understanding the basics of trigonometry and its applications in solving real-world problems. It is essential for students to have a good grasp of these concepts to excel in higher-level mathematics and science courses.