| Step |
Hyp |
Ref |
Expression |
| 1 |
|
itgsincmulx.a |
|- ( ph -> A e. CC ) |
| 2 |
|
itgsincmulx.an0 |
|- ( ph -> A =/= 0 ) |
| 3 |
|
itgsincmulx.b |
|- ( ph -> B e. RR ) |
| 4 |
|
itgsincmulx.c |
|- ( ph -> C e. RR ) |
| 5 |
|
itgsincmulx.blec |
|- ( ph -> B <_ C ) |
| 6 |
|
eqid |
|- ( y e. CC |-> ( -u ( cos ` ( A x. y ) ) / A ) ) = ( y e. CC |-> ( -u ( cos ` ( A x. y ) ) / A ) ) |
| 7 |
1
|
adantr |
|- ( ( ph /\ y e. CC ) -> A e. CC ) |
| 8 |
|
simpr |
|- ( ( ph /\ y e. CC ) -> y e. CC ) |
| 9 |
7 8
|
mulcld |
|- ( ( ph /\ y e. CC ) -> ( A x. y ) e. CC ) |
| 10 |
9
|
coscld |
|- ( ( ph /\ y e. CC ) -> ( cos ` ( A x. y ) ) e. CC ) |
| 11 |
10
|
negcld |
|- ( ( ph /\ y e. CC ) -> -u ( cos ` ( A x. y ) ) e. CC ) |
| 12 |
2
|
adantr |
|- ( ( ph /\ y e. CC ) -> A =/= 0 ) |
| 13 |
11 7 12
|
divcld |
|- ( ( ph /\ y e. CC ) -> ( -u ( cos ` ( A x. y ) ) / A ) e. CC ) |
| 14 |
|
cnelprrecn |
|- CC e. { RR , CC } |
| 15 |
14
|
a1i |
|- ( ph -> CC e. { RR , CC } ) |
| 16 |
9
|
sincld |
|- ( ( ph /\ y e. CC ) -> ( sin ` ( A x. y ) ) e. CC ) |
| 17 |
16
|
negcld |
|- ( ( ph /\ y e. CC ) -> -u ( sin ` ( A x. y ) ) e. CC ) |
| 18 |
7 17
|
mulcld |
|- ( ( ph /\ y e. CC ) -> ( A x. -u ( sin ` ( A x. y ) ) ) e. CC ) |
| 19 |
18
|
negcld |
|- ( ( ph /\ y e. CC ) -> -u ( A x. -u ( sin ` ( A x. y ) ) ) e. CC ) |
| 20 |
|
dvcosax |
|- ( A e. CC -> ( CC _D ( y e. CC |-> ( cos ` ( A x. y ) ) ) ) = ( y e. CC |-> ( A x. -u ( sin ` ( A x. y ) ) ) ) ) |
| 21 |
1 20
|
syl |
|- ( ph -> ( CC _D ( y e. CC |-> ( cos ` ( A x. y ) ) ) ) = ( y e. CC |-> ( A x. -u ( sin ` ( A x. y ) ) ) ) ) |
| 22 |
15 10 18 21
|
dvmptneg |
|- ( ph -> ( CC _D ( y e. CC |-> -u ( cos ` ( A x. y ) ) ) ) = ( y e. CC |-> -u ( A x. -u ( sin ` ( A x. y ) ) ) ) ) |
| 23 |
15 11 19 22 1 2
|
dvmptdivc |
|- ( ph -> ( CC _D ( y e. CC |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) = ( y e. CC |-> ( -u ( A x. -u ( sin ` ( A x. y ) ) ) / A ) ) ) |
| 24 |
18 7 12
|
divnegd |
|- ( ( ph /\ y e. CC ) -> -u ( ( A x. -u ( sin ` ( A x. y ) ) ) / A ) = ( -u ( A x. -u ( sin ` ( A x. y ) ) ) / A ) ) |
| 25 |
24
|
eqcomd |
|- ( ( ph /\ y e. CC ) -> ( -u ( A x. -u ( sin ` ( A x. y ) ) ) / A ) = -u ( ( A x. -u ( sin ` ( A x. y ) ) ) / A ) ) |
| 26 |
17 7 12
|
divcan3d |
|- ( ( ph /\ y e. CC ) -> ( ( A x. -u ( sin ` ( A x. y ) ) ) / A ) = -u ( sin ` ( A x. y ) ) ) |
| 27 |
26
|
negeqd |
|- ( ( ph /\ y e. CC ) -> -u ( ( A x. -u ( sin ` ( A x. y ) ) ) / A ) = -u -u ( sin ` ( A x. y ) ) ) |
| 28 |
16
|
negnegd |
|- ( ( ph /\ y e. CC ) -> -u -u ( sin ` ( A x. y ) ) = ( sin ` ( A x. y ) ) ) |
| 29 |
25 27 28
|
3eqtrd |
|- ( ( ph /\ y e. CC ) -> ( -u ( A x. -u ( sin ` ( A x. y ) ) ) / A ) = ( sin ` ( A x. y ) ) ) |
| 30 |
29
|
mpteq2dva |
|- ( ph -> ( y e. CC |-> ( -u ( A x. -u ( sin ` ( A x. y ) ) ) / A ) ) = ( y e. CC |-> ( sin ` ( A x. y ) ) ) ) |
| 31 |
23 30
|
eqtrd |
|- ( ph -> ( CC _D ( y e. CC |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) = ( y e. CC |-> ( sin ` ( A x. y ) ) ) ) |
| 32 |
6 13 31 16 3 4
|
dvmptresicc |
|- ( ph -> ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) = ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) ) |
| 33 |
32
|
fveq1d |
|- ( ph -> ( ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) ` x ) = ( ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) ` x ) ) |
| 34 |
33
|
adantr |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) ` x ) = ( ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) ` x ) ) |
| 35 |
|
eqidd |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) = ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) ) |
| 36 |
|
oveq2 |
|- ( y = x -> ( A x. y ) = ( A x. x ) ) |
| 37 |
36
|
fveq2d |
|- ( y = x -> ( sin ` ( A x. y ) ) = ( sin ` ( A x. x ) ) ) |
| 38 |
37
|
adantl |
|- ( ( ( ph /\ x e. ( B (,) C ) ) /\ y = x ) -> ( sin ` ( A x. y ) ) = ( sin ` ( A x. x ) ) ) |
| 39 |
|
simpr |
|- ( ( ph /\ x e. ( B (,) C ) ) -> x e. ( B (,) C ) ) |
| 40 |
1
|
adantr |
|- ( ( ph /\ x e. ( B (,) C ) ) -> A e. CC ) |
| 41 |
|
ioosscn |
|- ( B (,) C ) C_ CC |
| 42 |
41 39
|
sselid |
|- ( ( ph /\ x e. ( B (,) C ) ) -> x e. CC ) |
| 43 |
40 42
|
mulcld |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( A x. x ) e. CC ) |
| 44 |
43
|
sincld |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( sin ` ( A x. x ) ) e. CC ) |
| 45 |
35 38 39 44
|
fvmptd |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) ` x ) = ( sin ` ( A x. x ) ) ) |
| 46 |
34 45
|
eqtr2d |
|- ( ( ph /\ x e. ( B (,) C ) ) -> ( sin ` ( A x. x ) ) = ( ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) ` x ) ) |
| 47 |
46
|
itgeq2dv |
|- ( ph -> S. ( B (,) C ) ( sin ` ( A x. x ) ) _d x = S. ( B (,) C ) ( ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) ` x ) _d x ) |
| 48 |
|
sincn |
|- sin e. ( CC -cn-> CC ) |
| 49 |
48
|
a1i |
|- ( ph -> sin e. ( CC -cn-> CC ) ) |
| 50 |
41
|
a1i |
|- ( ph -> ( B (,) C ) C_ CC ) |
| 51 |
|
ssid |
|- CC C_ CC |
| 52 |
51
|
a1i |
|- ( ph -> CC C_ CC ) |
| 53 |
50 1 52
|
constcncfg |
|- ( ph -> ( y e. ( B (,) C ) |-> A ) e. ( ( B (,) C ) -cn-> CC ) ) |
| 54 |
50 52
|
idcncfg |
|- ( ph -> ( y e. ( B (,) C ) |-> y ) e. ( ( B (,) C ) -cn-> CC ) ) |
| 55 |
53 54
|
mulcncf |
|- ( ph -> ( y e. ( B (,) C ) |-> ( A x. y ) ) e. ( ( B (,) C ) -cn-> CC ) ) |
| 56 |
49 55
|
cncfmpt1f |
|- ( ph -> ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) e. ( ( B (,) C ) -cn-> CC ) ) |
| 57 |
32 56
|
eqeltrd |
|- ( ph -> ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) e. ( ( B (,) C ) -cn-> CC ) ) |
| 58 |
|
ioossicc |
|- ( B (,) C ) C_ ( B [,] C ) |
| 59 |
58
|
a1i |
|- ( ph -> ( B (,) C ) C_ ( B [,] C ) ) |
| 60 |
|
ioombl |
|- ( B (,) C ) e. dom vol |
| 61 |
60
|
a1i |
|- ( ph -> ( B (,) C ) e. dom vol ) |
| 62 |
1
|
adantr |
|- ( ( ph /\ y e. ( B [,] C ) ) -> A e. CC ) |
| 63 |
3 4
|
iccssred |
|- ( ph -> ( B [,] C ) C_ RR ) |
| 64 |
|
ax-resscn |
|- RR C_ CC |
| 65 |
63 64
|
sstrdi |
|- ( ph -> ( B [,] C ) C_ CC ) |
| 66 |
65
|
sselda |
|- ( ( ph /\ y e. ( B [,] C ) ) -> y e. CC ) |
| 67 |
62 66
|
mulcld |
|- ( ( ph /\ y e. ( B [,] C ) ) -> ( A x. y ) e. CC ) |
| 68 |
67
|
sincld |
|- ( ( ph /\ y e. ( B [,] C ) ) -> ( sin ` ( A x. y ) ) e. CC ) |
| 69 |
65 1 52
|
constcncfg |
|- ( ph -> ( y e. ( B [,] C ) |-> A ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 70 |
65 52
|
idcncfg |
|- ( ph -> ( y e. ( B [,] C ) |-> y ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 71 |
69 70
|
mulcncf |
|- ( ph -> ( y e. ( B [,] C ) |-> ( A x. y ) ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 72 |
49 71
|
cncfmpt1f |
|- ( ph -> ( y e. ( B [,] C ) |-> ( sin ` ( A x. y ) ) ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 73 |
|
cniccibl |
|- ( ( B e. RR /\ C e. RR /\ ( y e. ( B [,] C ) |-> ( sin ` ( A x. y ) ) ) e. ( ( B [,] C ) -cn-> CC ) ) -> ( y e. ( B [,] C ) |-> ( sin ` ( A x. y ) ) ) e. L^1 ) |
| 74 |
3 4 72 73
|
syl3anc |
|- ( ph -> ( y e. ( B [,] C ) |-> ( sin ` ( A x. y ) ) ) e. L^1 ) |
| 75 |
59 61 68 74
|
iblss |
|- ( ph -> ( y e. ( B (,) C ) |-> ( sin ` ( A x. y ) ) ) e. L^1 ) |
| 76 |
32 75
|
eqeltrd |
|- ( ph -> ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) e. L^1 ) |
| 77 |
|
coscn |
|- cos e. ( CC -cn-> CC ) |
| 78 |
77
|
a1i |
|- ( ph -> cos e. ( CC -cn-> CC ) ) |
| 79 |
78 71
|
cncfmpt1f |
|- ( ph -> ( y e. ( B [,] C ) |-> ( cos ` ( A x. y ) ) ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 80 |
79
|
negcncfg |
|- ( ph -> ( y e. ( B [,] C ) |-> -u ( cos ` ( A x. y ) ) ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 81 |
2
|
neneqd |
|- ( ph -> -. A = 0 ) |
| 82 |
|
elsng |
|- ( A e. CC -> ( A e. { 0 } <-> A = 0 ) ) |
| 83 |
1 82
|
syl |
|- ( ph -> ( A e. { 0 } <-> A = 0 ) ) |
| 84 |
81 83
|
mtbird |
|- ( ph -> -. A e. { 0 } ) |
| 85 |
1 84
|
eldifd |
|- ( ph -> A e. ( CC \ { 0 } ) ) |
| 86 |
|
difssd |
|- ( ph -> ( CC \ { 0 } ) C_ CC ) |
| 87 |
65 85 86
|
constcncfg |
|- ( ph -> ( y e. ( B [,] C ) |-> A ) e. ( ( B [,] C ) -cn-> ( CC \ { 0 } ) ) ) |
| 88 |
80 87
|
divcncf |
|- ( ph -> ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) e. ( ( B [,] C ) -cn-> CC ) ) |
| 89 |
3 4 5 57 76 88
|
ftc2 |
|- ( ph -> S. ( B (,) C ) ( ( RR _D ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) ` x ) _d x = ( ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` C ) - ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` B ) ) ) |
| 90 |
|
eqidd |
|- ( ph -> ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) = ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ) |
| 91 |
|
oveq2 |
|- ( y = C -> ( A x. y ) = ( A x. C ) ) |
| 92 |
91
|
fveq2d |
|- ( y = C -> ( cos ` ( A x. y ) ) = ( cos ` ( A x. C ) ) ) |
| 93 |
92
|
negeqd |
|- ( y = C -> -u ( cos ` ( A x. y ) ) = -u ( cos ` ( A x. C ) ) ) |
| 94 |
93
|
oveq1d |
|- ( y = C -> ( -u ( cos ` ( A x. y ) ) / A ) = ( -u ( cos ` ( A x. C ) ) / A ) ) |
| 95 |
94
|
adantl |
|- ( ( ph /\ y = C ) -> ( -u ( cos ` ( A x. y ) ) / A ) = ( -u ( cos ` ( A x. C ) ) / A ) ) |
| 96 |
3
|
rexrd |
|- ( ph -> B e. RR* ) |
| 97 |
4
|
rexrd |
|- ( ph -> C e. RR* ) |
| 98 |
|
ubicc2 |
|- ( ( B e. RR* /\ C e. RR* /\ B <_ C ) -> C e. ( B [,] C ) ) |
| 99 |
96 97 5 98
|
syl3anc |
|- ( ph -> C e. ( B [,] C ) ) |
| 100 |
|
ovexd |
|- ( ph -> ( -u ( cos ` ( A x. C ) ) / A ) e. _V ) |
| 101 |
90 95 99 100
|
fvmptd |
|- ( ph -> ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` C ) = ( -u ( cos ` ( A x. C ) ) / A ) ) |
| 102 |
|
oveq2 |
|- ( y = B -> ( A x. y ) = ( A x. B ) ) |
| 103 |
102
|
fveq2d |
|- ( y = B -> ( cos ` ( A x. y ) ) = ( cos ` ( A x. B ) ) ) |
| 104 |
103
|
negeqd |
|- ( y = B -> -u ( cos ` ( A x. y ) ) = -u ( cos ` ( A x. B ) ) ) |
| 105 |
104
|
oveq1d |
|- ( y = B -> ( -u ( cos ` ( A x. y ) ) / A ) = ( -u ( cos ` ( A x. B ) ) / A ) ) |
| 106 |
105
|
adantl |
|- ( ( ph /\ y = B ) -> ( -u ( cos ` ( A x. y ) ) / A ) = ( -u ( cos ` ( A x. B ) ) / A ) ) |
| 107 |
|
lbicc2 |
|- ( ( B e. RR* /\ C e. RR* /\ B <_ C ) -> B e. ( B [,] C ) ) |
| 108 |
96 97 5 107
|
syl3anc |
|- ( ph -> B e. ( B [,] C ) ) |
| 109 |
|
ovexd |
|- ( ph -> ( -u ( cos ` ( A x. B ) ) / A ) e. _V ) |
| 110 |
90 106 108 109
|
fvmptd |
|- ( ph -> ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` B ) = ( -u ( cos ` ( A x. B ) ) / A ) ) |
| 111 |
101 110
|
oveq12d |
|- ( ph -> ( ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` C ) - ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` B ) ) = ( ( -u ( cos ` ( A x. C ) ) / A ) - ( -u ( cos ` ( A x. B ) ) / A ) ) ) |
| 112 |
3
|
recnd |
|- ( ph -> B e. CC ) |
| 113 |
1 112
|
mulcld |
|- ( ph -> ( A x. B ) e. CC ) |
| 114 |
113
|
coscld |
|- ( ph -> ( cos ` ( A x. B ) ) e. CC ) |
| 115 |
114 1 2
|
divnegd |
|- ( ph -> -u ( ( cos ` ( A x. B ) ) / A ) = ( -u ( cos ` ( A x. B ) ) / A ) ) |
| 116 |
115
|
eqcomd |
|- ( ph -> ( -u ( cos ` ( A x. B ) ) / A ) = -u ( ( cos ` ( A x. B ) ) / A ) ) |
| 117 |
116
|
oveq2d |
|- ( ph -> ( ( -u ( cos ` ( A x. C ) ) / A ) - ( -u ( cos ` ( A x. B ) ) / A ) ) = ( ( -u ( cos ` ( A x. C ) ) / A ) - -u ( ( cos ` ( A x. B ) ) / A ) ) ) |
| 118 |
4
|
recnd |
|- ( ph -> C e. CC ) |
| 119 |
1 118
|
mulcld |
|- ( ph -> ( A x. C ) e. CC ) |
| 120 |
119
|
coscld |
|- ( ph -> ( cos ` ( A x. C ) ) e. CC ) |
| 121 |
120
|
negcld |
|- ( ph -> -u ( cos ` ( A x. C ) ) e. CC ) |
| 122 |
121 1 2
|
divcld |
|- ( ph -> ( -u ( cos ` ( A x. C ) ) / A ) e. CC ) |
| 123 |
114 1 2
|
divcld |
|- ( ph -> ( ( cos ` ( A x. B ) ) / A ) e. CC ) |
| 124 |
122 123
|
subnegd |
|- ( ph -> ( ( -u ( cos ` ( A x. C ) ) / A ) - -u ( ( cos ` ( A x. B ) ) / A ) ) = ( ( -u ( cos ` ( A x. C ) ) / A ) + ( ( cos ` ( A x. B ) ) / A ) ) ) |
| 125 |
111 117 124
|
3eqtrd |
|- ( ph -> ( ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` C ) - ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` B ) ) = ( ( -u ( cos ` ( A x. C ) ) / A ) + ( ( cos ` ( A x. B ) ) / A ) ) ) |
| 126 |
122 123
|
addcomd |
|- ( ph -> ( ( -u ( cos ` ( A x. C ) ) / A ) + ( ( cos ` ( A x. B ) ) / A ) ) = ( ( ( cos ` ( A x. B ) ) / A ) + ( -u ( cos ` ( A x. C ) ) / A ) ) ) |
| 127 |
120 1 2
|
divnegd |
|- ( ph -> -u ( ( cos ` ( A x. C ) ) / A ) = ( -u ( cos ` ( A x. C ) ) / A ) ) |
| 128 |
127
|
eqcomd |
|- ( ph -> ( -u ( cos ` ( A x. C ) ) / A ) = -u ( ( cos ` ( A x. C ) ) / A ) ) |
| 129 |
128
|
oveq2d |
|- ( ph -> ( ( ( cos ` ( A x. B ) ) / A ) + ( -u ( cos ` ( A x. C ) ) / A ) ) = ( ( ( cos ` ( A x. B ) ) / A ) + -u ( ( cos ` ( A x. C ) ) / A ) ) ) |
| 130 |
120 1 2
|
divcld |
|- ( ph -> ( ( cos ` ( A x. C ) ) / A ) e. CC ) |
| 131 |
123 130
|
negsubd |
|- ( ph -> ( ( ( cos ` ( A x. B ) ) / A ) + -u ( ( cos ` ( A x. C ) ) / A ) ) = ( ( ( cos ` ( A x. B ) ) / A ) - ( ( cos ` ( A x. C ) ) / A ) ) ) |
| 132 |
114 120 1 2
|
divsubdird |
|- ( ph -> ( ( ( cos ` ( A x. B ) ) - ( cos ` ( A x. C ) ) ) / A ) = ( ( ( cos ` ( A x. B ) ) / A ) - ( ( cos ` ( A x. C ) ) / A ) ) ) |
| 133 |
132
|
eqcomd |
|- ( ph -> ( ( ( cos ` ( A x. B ) ) / A ) - ( ( cos ` ( A x. C ) ) / A ) ) = ( ( ( cos ` ( A x. B ) ) - ( cos ` ( A x. C ) ) ) / A ) ) |
| 134 |
129 131 133
|
3eqtrd |
|- ( ph -> ( ( ( cos ` ( A x. B ) ) / A ) + ( -u ( cos ` ( A x. C ) ) / A ) ) = ( ( ( cos ` ( A x. B ) ) - ( cos ` ( A x. C ) ) ) / A ) ) |
| 135 |
125 126 134
|
3eqtrd |
|- ( ph -> ( ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` C ) - ( ( y e. ( B [,] C ) |-> ( -u ( cos ` ( A x. y ) ) / A ) ) ` B ) ) = ( ( ( cos ` ( A x. B ) ) - ( cos ` ( A x. C ) ) ) / A ) ) |
| 136 |
47 89 135
|
3eqtrd |
|- ( ph -> S. ( B (,) C ) ( sin ` ( A x. x ) ) _d x = ( ( ( cos ` ( A x. B ) ) - ( cos ` ( A x. C ) ) ) / A ) ) |