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Theorem sincos4thpi 8627
Description: The sine and cosine of pi / 4. (Contributed by Paul Chapman, 25-Jan-2008.)
Assertion
Ref Expression
sincos4thpi |- ((sin` (pi / 4)) = (1 / (sqr` 2)) /\ (cos` (pi / 4)) = (1 / (sqr` 2)))

Proof of Theorem sincos4thpi
StepHypRef Expression
1 2re 5926 . . . . . . . . . . . 12 |- 2 e. RR
2 2ne0 5937 . . . . . . . . . . . 12 |- 2 =/= 0
31, 2rereccl 5757 . . . . . . . . . . 11 |- (1 / 2) e. RR
43recn 5286 . . . . . . . . . 10 |- (1 / 2) e. CC
5 ax1cn 5241 . . . . . . . . . . 11 |- 1 e. CC
6 2halvest 5986 . . . . . . . . . . 11 |- (1 e. CC -> ((1 / 2) + (1 / 2)) = 1)
75, 6ax-mp 7 . . . . . . . . . 10 |- ((1 / 2) + (1 / 2)) = 1
8 sincosq1eq 8626 . . . . . . . . . 10 |- (((1 / 2) e. CC /\ (1 / 2) e. CC /\ ((1 / 2) + (1 / 2)) = 1) -> (sin`
((1 / 2) x. (pi / 2))) = (cos` ((1 / 2) x. (pi / 2))))
94, 4, 7, 8mp3an 913 . . . . . . . . 9 |- (sin` ((1 / 2) x. (pi / 2))) = (cos` ((1 / 2) x. (pi / 2)))
109opreq2i 3957 . . . . . . . 8 |- ((sin` ((1 / 2) x. (pi / 2))) x. (sin`
((1 / 2) x. (pi / 2)))) = ((sin`
((1 / 2) x. (pi / 2))) x. (cos` ((1 / 2) x. (pi / 2))))
1110opreq2i 3957 . . . . . . 7 |- (2 x. ((sin` ((1 / 2) x. (pi / 2))) x. (sin` ((1 / 2) x. (pi / 2))))) = (2 x. ((sin` ((1 / 2) x. (pi / 2))) x. (cos` ((1 / 2) x. (pi / 2)))))
12 2cn 5927 . . . . . . . . . . . 12 |- 2 e. CC
13 pire 8596 . . . . . . . . . . . . 13 |- pi e. RR
1413recn 5286 . . . . . . . . . . . 12 |- pi e. CC
155, 12, 14, 12, 2, 2divmuldiv 5742 . . . . . . . . . . 11 |- ((1 / 2) x. (pi / 2)) = ((1 x. pi) / (2 x. 2))
1614mulid2 5305 . . . . . . . . . . . 12 |- (1 x. pi) = pi
17 2t2e4 5969 . . . . . . . . . . . 12 |- (2 x. 2) = 4
1816, 17opreq12i 3958 . . . . . . . . . . 11 |- ((1 x. pi) / (2 x. 2)) = (pi / 4)
1915, 18eqtr 1487 . . . . . . . . . 10 |- ((1 / 2) x. (pi / 2)) = (pi / 4)
2019fveq2i 3712 . . . . . . . . 9 |- (sin` ((1 / 2) x. (pi / 2))) = (sin` (pi / 4))
2120, 20opreq12i 3958 . . . . . . . 8 |- ((sin` ((1 / 2) x. (pi / 2))) x. (sin`
((1 / 2) x. (pi / 2)))) = ((sin`
(pi / 4)) x. (sin` (pi / 4)))
2221opreq2i 3957 . . . . . . 7 |- (2 x. ((sin` ((1 / 2) x. (pi / 2))) x. (sin` ((1 / 2) x. (pi / 2))))) = (2 x. ((sin` (pi / 4)) x. (sin` (pi / 4))))
2312, 2recid 5696 . . . . . . . . . . 11 |- (2 x. (1 / 2)) = 1
2423opreq1i 3956 . . . . . . . . . 10 |- ((2 x. (1 / 2)) x. (pi / 2)) = (1 x. (pi / 2))
2513, 1, 2redivcl 5754 . . . . . . . . . . . 12 |- (pi / 2) e. RR
2625recn 5286 . . . . . . . . . . 11 |- (pi / 2) e. CC
2712, 4, 26mulass 5297 . . . . . . . . . 10 |- ((2 x. (1 / 2)) x. (pi / 2)) = (2 x. ((1 / 2) x. (pi / 2)))
2826mulid2 5305 . . . . . . . . . 10 |- (1 x. (pi / 2)) = (pi / 2)
2924, 27, 283eqtr3 1495 . . . . . . . . 9 |- (2 x. ((1 / 2) x. (pi / 2))) = (pi / 2)
3029fveq2i 3712 . . . . . . . 8 |- (sin` (2 x. ((1 / 2) x. (pi / 2)))) = (sin` (pi / 2))
314, 26mulcl 5293 . . . . . . . . 9 |- ((1 / 2) x. (pi / 2)) e. CC
32 sin2tt 7404 . . . . . . . . 9 |- (((1 / 2) x. (pi / 2)) e. CC -> (sin` (2 x. ((1 / 2) x. (pi / 2)))) = (2 x. ((sin`
((1 / 2) x. (pi / 2))) x. (cos` ((1 / 2) x. (pi / 2))))))
3331, 32ax-mp 7 . . . . . . . 8 |- (sin` (2 x. ((1 / 2) x. (pi / 2)))) = (2 x. ((sin` ((1 / 2) x. (pi / 2))) x. (cos`
((1 / 2) x. (pi / 2)))))
34 sinhalfpi 8599 . . . . . . . 8 |- (sin` (pi / 2)) = 1
3530, 33, 343eqtr3 1495 . . . . . . 7 |- (2 x. ((sin` ((1 / 2) x. (pi / 2))) x. (cos` ((1 / 2) x. (pi / 2))))) = 1
3611, 22, 353eqtr3 1495 . . . . . 6 |- (2 x. ((sin` (pi / 4)) x. (sin` (pi / 4)))) = 1
3736fveq2i 3712 . . . . 5 |- (sqr` (2 x. ((sin` (pi / 4)) x. (sin` (pi / 4))))) = (sqr` 1)
38 4re 5929 . . . . . . . . 9 |- 4 e. RR
39 4pos 5939 . . . . . . . . . 10 |- 0 < 4
4038, 39gt0ne0i 5591 . . . . . . . . 9 |- 4 =/= 0
4113, 38, 40redivcl 5754 . . . . . . . 8 |- (pi / 4) e. RR
42 resinclt 7380 . . . . . . . 8 |- ((pi / 4) e. RR -> (sin` (pi / 4)) e. RR)
4341, 42ax-mp 7 . . . . . . 7 |- (sin` (pi / 4)) e. RR
4443, 43remulcl 5307 . . . . . 6 |- ((sin` (pi / 4)) x. (sin`
(pi / 4))) e. RR
45 0re 5412 . . . . . . 7 |- 0 e. RR
46 2pos 5936 . . . . . . 7 |- 0 < 2
4745, 1, 46ltlei 5554 . . . . . 6 |- 0 <_ 2
4843msqge0 5588 . . . . . 6 |- 0 <_ ((sin` (pi / 4)) x. (sin` (pi / 4)))
491, 44, 47, 48sqrmuli 6634 . . . . 5 |- (sqr` (2 x. ((sin` (pi / 4)) x. (sin` (pi / 4))))) = ((sqr` 2) x. (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))))
50 sqr1 6646 . . . . 5 |- (sqr` 1) = 1
5137, 49, 503eqtr3r 1496 . . . 4 |- 1 = ((sqr`
2) x. (sqr` ((sin` (pi / 4)) x. (sin`
(pi / 4)))))
52 sqr2re 6660 . . . . . 6 |- (sqr` 2) e. RR
5352recn 5286 . . . . 5 |- (sqr` 2) e. CC
54 sqrclt 6640 . . . . . . 7 |- ((((sin`
(pi / 4)) x. (sin` (pi / 4))) e. RR /\ 0 <_ ((sin` (pi / 4)) x. (sin`
(pi / 4)))) -> (sqr`
((sin`
(pi / 4)) x. (sin` (pi / 4)))) e. RR)
5544, 48, 54mp2an 695 . . . . . 6 |- (sqr` ((sin`
(pi / 4)) x. (sin` (pi / 4)))) e. RR
5655recn 5286 . . . . 5 |- (sqr` ((sin`
(pi / 4)) x. (sin` (pi / 4)))) e. CC
57 sqr00t 6644 . . . . . . . . 9 |- ((2 e. RR /\ 0 <_ 2) -> ((sqr` 2) = 0 <-> 2 = 0))
581, 47, 57mp2an 695 . . . . . . . 8 |- ((sqr` 2) = 0 <-> 2 = 0)
5958necon3bii 1590 . . . . . . 7 |- ((sqr` 2) =/= 0 <-> 2 =/= 0)
602, 59mpbir 190 . . . . . 6 |- (sqr` 2) =/= 0
61 divmul2t 5677 . . . . . 6 |- (((1 e. CC /\ (sqr`
2) e. CC /\ (sqr`
((sin`
(pi / 4)) x. (sin` (pi / 4)))) e. CC) /\ (sqr` 2) =/= 0) -> ((1 / (sqr` 2)) = (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))) <-> 1 = ((sqr` 2) x. (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))))))
6260, 61mpan2 694 . . . . 5 |- ((1 e. CC /\ (sqr` 2) e. CC /\ (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))) e. CC) -> ((1 / (sqr`
2)) = (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))) <-> 1 = ((sqr` 2) x. (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))))))
635, 53, 56, 62mp3an 913 . . . 4 |- ((1 / (sqr` 2)) = (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4)))) <-> 1 = ((sqr` 2) x. (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4))))))
6451, 63mpbir 190 . . 3 |- (1 / (sqr`
2)) = (sqr` ((sin` (pi / 4)) x. (sin` (pi / 4))))
65 pipos 8597 . . . . . . . 8 |- 0 < pi
6613, 38, 65, 39divgt0i 5814 . . . . . . 7 |- 0 < (pi / 4)
67 1re 5407 . . . . . . . 8 |- 1 e. RR
68 pigt2lt4 8594 . . . . . . . . . . 11 |- (2 < pi /\ pi < 4)
6968pm3.27i 324 . . . . . . . . . 10 |- pi < 4
7013, 38, 38, 39ltdiv1i 5779 . . . . . . . . . 10 |- (pi < 4 <-> (pi / 4) < (4 / 4))
7169, 70mpbi 189 . . . . . . . . 9 |- (pi / 4) < (4 / 4)
7238recn 5286 . . . . . . . . . 10 |- 4 e. CC
7372, 40divid 5726 . . . . . . . . 9 |- (4 / 4) = 1
7471, 73breqtr 2628 . . . . . . . 8 |- (pi / 4) < 1
7541, 67, 74ltlei 5554 . . . . . . 7 |- (pi / 4) <_ 1
76 elioc2t 6322 . . . . . . . . 9 |- ((0 e.