let Z be open Subset of REAL; :: thesis: ( Z c= dom (sec * arccot) & Z c= ].(- 1),1.[ implies ( sec * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) ) ) )
assume that
A1: Z c= dom (sec * arccot) and
A2: Z c= ].(- 1),1.[ ; :: thesis: ( sec * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) ) )
A3: for x being Real st x in Z holds
cos . (arccot . x) <> 0

proof

let x be Real; :: thesis: ( x in Z implies cos . (arccot . x) <> 0 )
assume x in Z ; :: thesis: cos . (arccot . x) <> 0
then arccot . x in dom sec by A1, FUNCT_1:11;
hence cos . (arccot . x) <> 0 by RFUNCT_1:3; :: thesis: verum

end;

A4: for x being Real st x in Z holds
sec * arccot is_differentiable_in x

proof

let x be Real; :: thesis: ( x in Z implies sec * arccot is_differentiable_in x )
assume A5: x in Z ; :: thesis: sec * arccot is_differentiable_in x
then cos . (arccot . x) <> 0 by A3;
then A6: sec is_differentiable_in arccot . x by FDIFF_9:1;
arccot is_differentiable_on Z by A2, SIN_COS9:82;
then arccot is_differentiable_in x by A5, FDIFF_1:9;
hence sec * arccot is_differentiable_in x by A6, FDIFF_2:13; :: thesis: verum

end;

then A7: sec * arccot is_differentiable_on Z by A1, FDIFF_1:9;
for x being Real st x in Z holds
((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2))))

proof

let x be Real; :: thesis: ( x in Z implies ((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) )
assume A8: x in Z ; :: thesis: ((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2))))
then A9: cos . (arccot . x) <> 0 by A3;
cos . (arccot . x) <> 0 by A3, A8;
then A10: sec is_differentiable_in arccot . x by FDIFF_9:1;
A11: arccot is_differentiable_on Z by A2, SIN_COS9:82;
then A12: arccot is_differentiable_in x by A8, FDIFF_1:9;
((sec * arccot) `| Z) . x = diff ((sec * arccot),x) by A7, A8, FDIFF_1:def 7
.= (diff (sec,(arccot . x))) * (diff (arccot,x)) by A12, A10, FDIFF_2:13
.= ((sin . (arccot . x)) / ((cos . (arccot . x)) ^2)) * (diff (arccot,x)) by A9, FDIFF_9:1
.= ((sin . (arccot . x)) / ((cos . (arccot . x)) ^2)) * ((arccot `| Z) . x) by A8, A11, FDIFF_1:def 7
.= ((sin . (arccot . x)) / ((cos . (arccot . x)) ^2)) * (- (1 / (1 + (x ^2)))) by A2, A8, SIN_COS9:82
.= - (((sin . (arccot . x)) / ((cos . (arccot . x)) ^2)) * (1 / (1 + (x ^2))))
.= - (((sin . (arccot . x)) * 1) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) by XCMPLX_1:76
.= - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) ;
hence ((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) ; :: thesis: verum

end;

hence ( sec * arccot is_differentiable_on Z & ( for x being Real st x in Z holds
((sec * arccot) `| Z) . x = - ((sin . (arccot . x)) / (((cos . (arccot . x)) ^2) * (1 + (x ^2)))) ) ) by A1, A4, FDIFF_1:9; :: thesis: verum