130 MATHEMATICAL FORMULAE AND ELLIPTIC FUNCTIONS 



INFINITE PRODUCTS 



6.50 



00 



i. sin x = x 



n 



n = i 



CO 



ft = I 



4. cosh x = 



n= o 



6.51 



00 



sin x TT x 



i. = I I cos 



x JLJL 2" 



6.52 



6.53 



i. cosh x cos y = 



2. cos # - cos y = 2 [ i 



(- S)*i Hf- 



6.55 The convergent infinite series: 



00 



I+Wi + tt2 + . .= I + ^W, 



