let a, b be Real; :: thesis: for Z being open Subset of REAL
for f being PartFunc of REAL ,REAL st Z c= dom (f (#) cot ) & ( for x being Real st x in Z holds
f . x = (a * x) + b ) holds
( f (#) cot is_differentiable_on Z & ( for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ) )
let Z be open Subset of REAL ; :: thesis: for f being PartFunc of REAL ,REAL st Z c= dom (f (#) cot ) & ( for x being Real st x in Z holds
f . x = (a * x) + b ) holds
( f (#) cot is_differentiable_on Z & ( for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ) )
let f be PartFunc of REAL ,REAL ; :: thesis: ( Z c= dom (f (#) cot ) & ( for x being Real st x in Z holds
f . x = (a * x) + b ) implies ( f (#) cot is_differentiable_on Z & ( for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ) ) )
assume that
A1: Z c= dom (f (#) cot ) and
A2: for x being Real st x in Z holds
f . x = (a * x) + b ; :: thesis: ( f (#) cot is_differentiable_on Z & ( for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ) )
A3: Z c= (dom f) /\ (dom cot ) by A1, VALUED_1:def 4;
then A4: Z c= dom cot by XBOOLE_1:18;
A5: Z c= dom f by A3, XBOOLE_1:18;
then A6: f is_differentiable_on Z by A2, FDIFF_1:31;
A7: for x being Real st x in Z holds
( cot is_differentiable_in x & diff cot ,x = - (1 / ((sin . x) ^2 )) )

proof

let x be Real; :: thesis: ( x in Z implies ( cot is_differentiable_in x & diff cot ,x = - (1 / ((sin . x) ^2 )) ) )
assume x in Z ; :: thesis: ( cot is_differentiable_in x & diff cot ,x = - (1 / ((sin . x) ^2 )) )
then sin . x <> 0 by A4, Th2;
hence ( cot is_differentiable_in x & diff cot ,x = - (1 / ((sin . x) ^2 )) ) by FDIFF_7:47; :: thesis: verum

end;

then for x being Real st x in Z holds
cot is_differentiable_in x ;
then A8: cot is_differentiable_on Z by A4, FDIFF_1:16;
for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 ))

proof

let x be Real; :: thesis: ( x in Z implies ((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) )
assume A9: x in Z ; :: thesis: ((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 ))
then ((f (#) cot ) `| Z) . x = ((cot . x) * (diff f,x)) + ((f . x) * (diff cot ,x)) by A1, A6, A8, FDIFF_1:29
.= ((cot . x) * ((f `| Z) . x)) + ((f . x) * (diff cot ,x)) by A6, A9, FDIFF_1:def 8
.= ((cot . x) * a) + ((f . x) * (diff cot ,x)) by A2, A5, A9, FDIFF_1:31
.= ((cot . x) * a) + (((a * x) + b) * (diff cot ,x)) by A2, A9
.= ((cot . x) * a) + (((a * x) + b) * (- (1 / ((sin . x) ^2 )))) by A7, A9
.= (((cos . x) / (sin . x)) * (a / 1)) - (((a * x) + b) / ((sin . x) ^2 )) by A4, A9, RFUNCT_1:def 4
.= ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ;
hence ((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ; :: thesis: verum

end;

hence ( f (#) cot is_differentiable_on Z & ( for x being Real st x in Z holds
((f (#) cot ) `| Z) . x = ((a * (cos . x)) / (sin . x)) - (((a * x) + b) / ((sin . x) ^2 )) ) ) by A1, A6, A8, FDIFF_1:29; :: thesis: verum