ML Aggarwal Solutions for Class 9 Maths Chapter 18 Trigonometric Ratios and Standard Angle

Trigonometric ratios are Sine, Cosine, Tangent, Cotangent, Secant and Cosecant. The standard angles for these trigonometric ratios are 0°, 30°, 45°, 60° and 90°. These angles can also be represented in the form of radians such as 0, π/6, π/4, π/3, and π/2. Two angles are said to be complementary if their sum is 90°. Thus θ and (90° – θ) are complementary angles. Trigonometric ratios of complementary angles help in simplifying problems. Representing complementary angles in terms of these standard angles helps in solving a complex problem involving trigonometric ratios.

A trigonometric equation is one that involves one or more of the six functions sine, cosine, tangent, cotangent, secant, and cosecant. It contains one or many trigonometric functions of the variable x. Solving for x means finding the value of x for which makes the trigonometric equation true.


Recall trigonometric ratios of some special angles; they play a major role in solving the trigonometric equations.