let Z be open Subset of REAL; :: thesis: ( Z c= dom (cos * arccot) & Z c= ].(- 1),1.[ implies ( cos * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2)) ) ) )
assume that
A1: Z c= dom (cos * arccot) and
A2: Z c= ].(- 1),1.[ ; :: thesis: ( cos * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2)) ) )
A3: for x being Real st x in Z holds
cos * arccot is_differentiable_in x

proof

let x be Real; :: thesis: ( x in Z implies cos * arccot is_differentiable_in x )
assume A4: x in Z ; :: thesis: cos * arccot is_differentiable_in x
A5: cos is_differentiable_in arccot . x by SIN_COS:63;
arccot is_differentiable_on Z by A2, SIN_COS9:82;
then arccot is_differentiable_in x by A4, FDIFF_1:9;
hence cos * arccot is_differentiable_in x by A5, FDIFF_2:13; :: thesis: verum

end;

then A6: cos * arccot is_differentiable_on Z by A1, FDIFF_1:9;
for x being Real st x in Z holds
((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2))

proof

let x be Real; :: thesis: ( x in Z implies ((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2)) )
assume A7: x in Z ; :: thesis: ((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2))
A8: arccot is_differentiable_on Z by A2, SIN_COS9:82;
then A9: arccot is_differentiable_in x by A7, FDIFF_1:9;
A10: cos is_differentiable_in arccot . x by SIN_COS:63;
((cos * arccot) `| Z) . x = diff ((cos * arccot),x) by A6, A7, FDIFF_1:def 7
.= (diff (cos,(arccot . x))) * (diff (arccot,x)) by A9, A10, FDIFF_2:13
.= (- (sin . (arccot . x))) * (diff (arccot,x)) by SIN_COS:63
.= - ((sin . (arccot . x)) * (diff (arccot,x)))
.= - ((sin . (arccot . x)) * ((arccot `| Z) . x)) by A7, A8, FDIFF_1:def 7
.= - ((sin . (arccot . x)) * (- (1 / (1 + (x ^2))))) by A2, A7, SIN_COS9:82
.= (sin . (arccot . x)) / (1 + (x ^2)) ;
hence ((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2)) ; :: thesis: verum

end;

hence ( cos * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((cos * arccot) `| Z) . x = (sin . (arccot . x)) / (1 + (x ^2)) ) ) by A1, A3, FDIFF_1:9; :: thesis: verum