Introduction to Trigonometry

This chapter introduces trigonometry through the ratios of the sides of a right-angled triangle. It defines the six trigonometric ratios (sine, cosine, tangent, cosecant, secant, cotangent) of an acute angle, derives their exact values for the standard angles 0°, 30°, 45°, 60° and 90°, establishes the fundamental trigonometric identities ($\sin^2\theta + \cos^2\theta = 1$ and its companions), and studies trigonometric ratios of complementary angles. It is a formula-rich, high-scoring chapter and a foundation for Applications of Trigonometry (heights and distances), important for both CBSE and State Board examinations.