Sine and cosine are less than unity, secant and cosecant are Definition of function. Each ratio can be expressed in terms of any of the others CASE II. When one side and one acute angle are given Case of triangle considered as sum or difference of two right- Definitions of the trigonometrical ratios of any angle. Signs of the trigonometrical ratios in the four quadrants Expansions of the sine and cosine of A+B and A - B sin (A+B) sin (A – B) = sin2 A – sin2 B. Value of sin 18° TRANSFORMATION OF PRODUCTS AND SUMS. Transformation of products into sums or differences Distances of in-centre and ex-centres from circum-centre Distance of orthocentre from circum-centre |