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Theorem sinq12gt0t 8625
Description: The sine of a number strictly between 0 and pi is positive. (Contributed by Paul Chapman, 15-Mar-2008.)
Assertion
Ref Expression
sinq12gt0t |- (A e. (0(,)pi) -> 0 < (sin` A))

Proof of Theorem sinq12gt0t
StepHypRef Expression
1 0re 5412 . . 3 |- 0 e. RR
2 pire 8596 . . 3 |- pi e. RR
3 elioo2t 6316 . . . 4 |- ((0 e. RR* /\ pi e. RR*) -> (A e. (0(,)pi) <-> (A e. RR /\ 0 < A /\ A < pi)))
4 rexrt 5471 . . . 4 |- (0 e. RR -> 0 e. RR*)
5 rexrt 5471 . . . 4 |- (pi e. RR -> pi e. RR*)
63, 4, 5syl2an 454 . . 3 |- ((0 e. RR /\ pi e. RR) -> (A e. (0(,)pi) <-> (A e. RR /\ 0 < A /\ A < pi)))
71, 2, 6mp2an 695 . 2 |- (A e. (0(,)pi) <-> (A e. RR /\ 0 < A /\ A < pi))
8 sincosq1lem 8620 . . . . 5 |- (((A / 2) e. RR /\ 0 < (A / 2) /\ (A / 2) < (pi / 2)) -> 0 < (sin` (A / 2)))
9 rehalfclt 5981 . . . . . 6 |- (A e. RR -> (A / 2) e. RR)
1093ad2ant1 798 . . . . 5 |- ((A e. RR /\ 0 < A /\ A < pi) -> (A / 2) e. RR)
11 halfpos2t 5984 . . . . . . 7 |- (A e. RR -> (0 < A <-> 0 < (A / 2)))
1211biimpa 416 . . . . . 6 |- ((A e. RR /\ 0 < A) -> 0 < (A / 2))
13123adant3 797 . . . . 5 |- ((A e. RR /\ 0 < A /\ A < pi) -> 0 < (A / 2))
14 2re 5926 . . . . . . . 8 |- 2 e. RR
15 2pos 5936 . . . . . . . . 9 |- 0 < 2
16 ltdiv1t 5805 . . . . . . . . 9 |- (((A e. RR /\ pi e. RR /\ 2 e. RR) /\ 0 < 2) -> (A < pi <-> (A / 2) < (pi / 2)))
1715, 16mpan2 694 . . . . . . . 8 |- ((A e. RR /\ pi e. RR /\ 2 e. RR) -> (A < pi <-> (A / 2) < (pi / 2)))
182, 14, 17mp3an23 905 . . . . . . 7 |- (A e. RR -> (A < pi <-> (A / 2) < (pi / 2)))
1918adantr 389 . . . . . 6 |- ((A e. RR /\ 0 < A) -> (A < pi <-> (A / 2) < (pi / 2)))
2019biimp3a 916 . . . . 5 |- ((A e. RR /\ 0 < A /\ A < pi) -> (A / 2) < (pi / 2))
218, 10, 13, 20syl3anc 856 . . . 4 |- ((A e. RR /\ 0 < A /\ A < pi) -> 0 < (sin` (A / 2)))
22 sincosq1lem 8620 . . . . . 6 |- ((((pi - A) / 2) e. RR /\ 0 < ((pi - A) / 2) /\ ((pi - A) / 2) < (pi / 2)) -> 0 < (sin` ((pi - A) / 2)))
23 resubclt 5410 . . . . . . . . 9 |- ((pi e. RR /\ A e. RR) -> (pi - A) e. RR)
242, 23mpan 693 . . . . . . . 8 |- (A e. RR -> (pi - A) e. RR)
25 rehalfclt 5981 . . . . . . . 8 |- ((pi - A) e. RR -> ((pi - A) / 2) e. RR)
2624, 25syl 10 . . . . . . 7 |- (A e. RR -> ((pi - A) / 2) e. RR)
27263ad2ant1 798 . . . . . 6 |- ((A e. RR /\ 0 < A /\ A < pi) -> ((pi - A) / 2) e. RR)
28 posdift 5627 . . . . . . . . . 10 |- ((A e. RR /\ pi e. RR) -> (A < pi <-> 0 < (pi - A)))
292, 28mpan2 694 . . . . . . . . 9 |- (A e. RR -> (A < pi <-> 0 < (pi - A)))
30 halfpos2t 5984 . . . . . . . . . 10 |- ((pi - A) e. RR -> (0 < (pi - A) <-> 0 < ((pi - A) / 2)))
3124, 30syl 10 . . . . . . . . 9 |- (A e. RR -> (0 < (pi - A) <-> 0 < ((pi - A) / 2)))
3229, 31bitrd 526 . . . . . . . 8 |- (A e. RR -> (A < pi <-> 0 < ((pi - A) / 2)))
3332adantr 389 . . . . . . 7 |- ((A e. RR /\ 0 < A) -> (A < pi <-> 0 < ((pi - A) / 2)))
3433biimp3a 916 . . . . . 6 |- ((A e. RR /\ 0 < A /\ A < pi) -> 0 < ((pi - A) / 2))
35 ltsubpost 5626 . . . . . . . . . 10 |- ((A e. RR /\ pi e. RR) -> (0 < A <-> (pi - A) < pi))
362, 35mpan2 694 . . . . . . . . 9 |- (A e. RR -> (0 < A <-> (pi - A) < pi))
37 ltdiv1t 5805 . . . . . . . . . . . 12 |- ((((pi - A) e. RR /\ pi e. RR /\ 2 e. RR) /\ 0 < 2) -> ((pi - A) < pi <-> ((pi - A) / 2) < (pi / 2)))
3815, 37mpan2 694 . . . . . . . . . . 11 |- (((pi - A) e. RR /\ pi e. RR /\ 2 e. RR) -> ((pi - A) < pi <-> ((pi - A) / 2) < (pi / 2)))
392, 14, 38mp3an23 905 . . . . . . . . . 10 |- ((pi - A) e. RR -> ((pi - A) < pi <-> ((pi - A) / 2) < (pi / 2)))
4024, 39syl 10 . . . . . . . . 9 |- (A e. RR -> ((pi - A) < pi <-> ((pi - A) / 2) < (pi / 2)))
4136, 40bitrd 526 . . . . . . . 8 |- (A e. RR -> (0 < A <-> ((pi - A) / 2) < (pi / 2)))
4241biimpa 416 . . . . . . 7 |- ((A e. RR /\ 0 < A) -> ((pi - A) / 2) < (pi / 2))
43423adant3 797 . . . . . 6 |- ((A e. RR /\ 0 < A /\ A < pi) -> ((pi - A) / 2) < (pi / 2))
4422, 27, 34, 43syl3anc 856 . . . . 5 |- ((A e. RR /\ 0 < A /\ A < pi) -> 0 < (sin` ((pi - A) / 2)))
45 recnt 5285 . . . . . . . . 9 |- (A e. RR -> A e. CC)
462recn 5286 . . . . . . . . . 10 |- pi e. CC
47 2cn 5927 . . . . . . . . . 10 |- 2 e. CC
48 2ne0 5937 . . . . . . . . . . 11 |- 2 =/= 0
49 divsubdirt 5731 . . . . . . . . . . 11 |- (((pi e. CC /\ A e. CC /\ 2 e. CC) /\ 2 =/= 0) -> ((pi - A) / 2) = ((pi / 2) - (A / 2)))
5048, 49mpan2 694 . . . . . . . . . 10 |- ((pi e. CC /\ A e. CC /\ 2 e. CC) -> ((pi - A) / 2) = ((pi / 2) - (A / 2)))
5146, 47, 50mp3an13 904 . . . . . . . . 9 |- (A e. CC -> ((pi - A) / 2) = ((pi / 2) - (A / 2)))
5245, 51syl 10 . . . . . . . 8 |- (A e. RR -> ((pi - A) / 2) = ((pi / 2) - (A / 2)))
5352fveq2d 3713 . . . . . . 7 |- (A e. RR -> (sin` ((pi - A) / 2)) = (sin` ((pi / 2) - (A / 2))))
549recnd 5287 . . . . . . . 8 |- (A e. RR -> (A / 2) e. CC)
55 sinhalfpim 8617 . . . . . . . 8 |- ((A / 2) e. CC -> (sin` ((pi / 2) - (A / 2))) = (cos`
(A / 2)))
5654, 55syl 10 . . . . . . 7 |- (A e. RR -> (sin` ((pi / 2) - (A / 2))) = (cos` (A / 2)))
5753, 56eqtrd 1499 . . . . . 6 |- (A e. RR -> (sin` ((pi - A) / 2)) = (cos` (A / 2)))
58573ad2ant1 798 . . . . 5 |- ((A e. RR /\ 0 < A /\ A < pi) -> (sin` ((pi - A) / 2)) = (cos` (A / 2)))
5944, 58breqtrd 2629 . . . 4 |- ((A e. RR /\ 0 < A /\ A < pi) -> 0 < (cos` (A / 2)))
60 resinclt 7380 . . . . . . . 8 |- ((A / 2) e. RR -> (sin` (A / 2)) e. RR)
61 recosclt 7381 . . . . . . . 8 |- ((A / 2) e. RR -> (cos` (A / 2)) e. RR)
6260, 61jca 288 . . . . . . 7 |- ((A / 2) e. RR -> ((sin` (A / 2)) e. RR /\ (cos` (A / 2)) e. RR))
63 axmulgt0 5478 . . . . . . 7 |- (((sin` (A / 2)) e. RR /\ (cos` (A / 2)) e. RR) -> ((0 < (sin`
(A / 2)) /\ 0 < (cos`
(A / 2))) -> 0 < ((sin` (A / 2)) x. (cos`
(A / 2)))))
649, 62, 633syl 20 . . . . . 6 |- (A e. RR -> ((0 < (sin` (A / 2)) /\ 0 < (cos` (A / 2))) -> 0 < ((sin`
(A / 2)) x. (cos` (A / 2)))))
65 axmulrcl 5246 . . . . . . . . 9 |- (((sin` (A / 2)) e. RR /\ (cos` (A / 2)) e. RR) -> ((sin` (A / 2)) x. (cos` (A / 2))) e. RR)
669, 62, 653syl 20 . . . . . . . 8 |- (A e. RR -> ((sin` (A / 2)) x. (cos` (A / 2))) e. RR)
67 axmulgt0 5478 . . . . . . . . 9 |- ((2 e. RR /\ ((sin`
(A / 2)) x. (cos` (A / 2))) e. RR) -> ((0 < 2 /\ 0 < ((sin` (A / 2)) x. (cos` (A / 2)))) -> 0 < (2 x. ((sin` (A / 2)) x. (cos` (A / 2))))))
6814, 67mpan 693 . . . . . . . 8 |- (((sin` (A / 2)) x. (cos` (A / 2))) e. RR -> ((0 < 2 /\ 0 < ((sin