theorem :: DIFF_3:72

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 + (h / 2)) <> 0 & sin (x - (h / 2)) <> 0 holds
(cD (f,h)) . x = ((((16 * (cos x)) * (sin ((- h) / 2))) * (cos ((- h) / 2))) * (sin x)) / (((cos (2 * x)) - (cos h)) ^2)