Trigonometry is defined as trigonon means triangle and metron means measurement or we can say trigonometry means the measurement of a triangle. A triangle is divided into six parts, 3sides and 3angles so to determine the relationship between sides and angles we need to study trigonometry. In JEE Mains or other engineering exams, trigonometry is the foundation of all the chapters. Every year you see at least 24 questions in those examinations. But this was the only data of direct questions from this chapter and will you imagine that in 2025% questions the concept of trigonometry is used. You are very well familiar with the basics of trigonometry as you already studied in previous classes now in this chapter you will learn interesting facts about trigonometry. The whole chapter revolves around three basic terms sine, cosine, and tangent including three parameters (a,b,c) or we can say sides of the triangle.
If we talk about the importance of this chapter, you will find that how questions can be tricked using trigonometry in Calculus, Matrices and Determinant, and Functions. Overall this chapter is directly or indirectly present in your whole textbook. So, you need to do proper practice, you should solve an ample amount of questions and make sure you are good with calculations.
Let us take a reallife example of Trigonometry,
In summer if you are out from your home, you always try to keep yourself within the shadow ( a tree or a building) but have you ever observed that in day time the shadow is small in size and at morning or evening shadow is large in size why this is happening, the size of building or tree is not changing even the sun's size is not changing?
The reason we studied or known to us is that the position of the sun is changing with respect to the earth.
Here the change in position is explained as the angle changes from 0º to 180º and at 90º the position of the sun is exactly above the object that's why their shadow becomes diminished and from 0º to 180º shadow starts first decreasing till 90º and starts increasing.
Let's take an application of Trigonometry
In the given figure if know the elevation angle and distance of the building you can easily calculate the height of the building using, .
After studying Trigonometry you will able to:
Important Topics:
Trigonometry Function and their Identities: In this topic, we learn a small and very important part of trigonometry, as every function have both a domain and a range so here we will study the range and domain of every trigonometry function and their behavior. The chapter explains all the identities formed with these functions. It is the first step to understanding trigonometry, and finally, multiconcept problems can be solve using these concepts.
Trigonometry Equation: This topic involves solving trigonometric equations, general solutions to all the trigonometric functions. This chapter has a lot of properties that are important to remember. The chapter contains the application of concepts that you learned in the previous chapters of trigonometry. If your basic is clear then there will be no issue for you to be perfect in this section.
Some Important General Solutions of Equations
Inverse Trigonometric functions: This chapter is very different from the above chapters and forms a greater part of trigonometry. In the above topic, you study the trig function associated angle with but in this topic, you will study angles associated with trig function. In simple words, it contains the inverse of the functions that you were learned in the first lesson.
For eg. \tan\theta=\frac{sin\theta}{cos\theta}\;\;\text{or,}\;\tan\theta=\frac{1}{cot\theta}
First, finish all the concepts, example and questions given in NCERT Maths Book along with Miscellaneous Exercise. You must be thorough with the concept of Trigonometry. Then you can refer to the book Algebra by Dr. SK goyal or RD Sharma but make sure you follow any one of these not all. Trigonometry is explained very well in these books and there are an ample amount of questions with crystal clear concepts. Choice of reference book depends on person to person, find the book that best suits you the best, depending on how well you are clear with the concepts and the difficulty of the questions you require.
Chapters 
Chapters Name 
Chapter 1 

Chapter 2 

Chapter 3 

Chapter 4 

Chapter 5 

Chapter 6 

Chapter 7 

Chapter 8 

Chapter 9 

Chapter 10 

Chapter 11 

Chapter 12 

Chapter 13 

Chapter 15 

Chapter 16 
If are in A.P. and are also in A.P. , then:
The angle of elevation of the top of a vertical tower from a point P on the horizontal ground was observed to be . After moving a distance 2 metres from P towards the foot of the tower, the angle of elevation changes to . Then the height (in metres) of the tower is :
Two ships A and B are sailing straight away from a fixed point O along routes such that AOB is always 120^{0}. At a certain instance, OA = 8 km, OB = 6 km and the ship A is sailing at the rate of 20 km/hr while the ship B sailing at the rate of 30 km/hr. Then the distance between A and B is changing at the rate (in km/hr) :