theorem :: DIFF_2:71

for x0, x1 being Real st x0 in dom cosec & x1 in dom cosec holds
[!cosec,x0,x1!] = ((2 * (cos ((x1 + x0) / 2))) * (sin ((x1 - x0) / 2))) / (((sin x1) * (sin x0)) * (x0 - x1))