let Z be open Subset of REAL; ( Z c= ].(- 1),1.[ implies ( cos (#) (arctan + arccot) is_differentiable_on Z & ( for x being Real st x in Z holds
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x))) ) ) )
for x being Real st x in Z holds
cos is_differentiable_in x
by SIN_COS:63;
then A1:
cos is_differentiable_on Z
by FDIFF_1:9, SIN_COS:24;
assume A2:
Z c= ].(- 1),1.[
; ( cos (#) (arctan + arccot) is_differentiable_on Z & ( for x being Real st x in Z holds
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x))) ) )
then A3:
arctan + arccot is_differentiable_on Z
by Th37;
A4:
].(- 1),1.[ c= [.(- 1),1.]
by XXREAL_1:25;
then
].(- 1),1.[ c= dom arccot
by SIN_COS9:24, XBOOLE_1:1;
then A5:
Z c= dom arccot
by A2, XBOOLE_1:1;
].(- 1),1.[ c= dom arctan
by A4, SIN_COS9:23, XBOOLE_1:1;
then
Z c= dom arctan
by A2, XBOOLE_1:1;
then
Z c= (dom arctan) /\ (dom arccot)
by A5, XBOOLE_1:19;
then A6:
Z c= dom (arctan + arccot)
by VALUED_1:def 1;
then
Z c= (dom cos) /\ (dom (arctan + arccot))
by SIN_COS:24, XBOOLE_1:19;
then A7:
Z c= dom (cos (#) (arctan + arccot))
by VALUED_1:def 4;
for x being Real st x in Z holds
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x)))
proof
let x be
Real;
( x in Z implies ((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x))) )
assume A8:
x in Z
;
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x)))
then ((cos (#) (arctan + arccot)) `| Z) . x =
(((arctan + arccot) . x) * (diff (cos,x))) + ((cos . x) * (diff ((arctan + arccot),x)))
by A7, A1, A3, FDIFF_1:21
.=
(((arctan . x) + (arccot . x)) * (diff (cos,x))) + ((cos . x) * (diff ((arctan + arccot),x)))
by A6, A8, VALUED_1:def 1
.=
(((arctan . x) + (arccot . x)) * (- (sin . x))) + ((cos . x) * (diff ((arctan + arccot),x)))
by SIN_COS:63
.=
(((arctan . x) + (arccot . x)) * (- (sin . x))) + ((cos . x) * (((arctan + arccot) `| Z) . x))
by A3, A8, FDIFF_1:def 7
.=
(- (((arctan . x) + (arccot . x)) * (sin . x))) + ((cos . x) * 0)
by A2, A8, Th37
.=
- ((sin . x) * ((arctan . x) + (arccot . x)))
;
hence
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x)))
;
verum
end;
hence
( cos (#) (arctan + arccot) is_differentiable_on Z & ( for x being Real st x in Z holds
((cos (#) (arctan + arccot)) `| Z) . x = - ((sin . x) * ((arctan . x) + (arccot . x))) ) )
by A7, A1, A3, FDIFF_1:21; verum