theorem :: DIFF_3:71

for h, x being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = 1 / ((sin x) ^2) ) & sin x <> 0 & sin (x - h) <> 0 holds
(bD (f,h)) . x = ((((16 * (cos (((2 * x) - h) / 2))) * (sin ((- h) / 2))) * (cos ((- h) / 2))) * (sin (((2 * x) - h) / 2))) / (((cos ((2 * x) - h)) - (cos h)) ^2)