theorem :: DIFF_3:93

for x0, x1 being Real
for f being Function of REAL,REAL st ( for x being Real holds f . x = (tan (#) tan) . x ) & x0 in dom tan & x1 in dom tan holds
[!f,x0,x1!] = (((cos x1) ^2) - ((cos x0) ^2)) / ((((cos x0) * (cos x1)) ^2) * (x0 - x1))