Metamath Proof Explorer


Theorem acosbnd

Description: The arccosine function has range within a vertical strip of the complex plane with real part between 0 and _pi . (Contributed by Mario Carneiro, 2-Apr-2015)

Ref Expression
Assertion acosbnd A arccos A 0 π

Proof

Step Hyp Ref Expression
1 acosval A arccos A = π 2 arcsin A
2 1 fveq2d A arccos A = π 2 arcsin A
3 halfpire π 2
4 3 recni π 2
5 asincl A arcsin A
6 resub π 2 arcsin A π 2 arcsin A = π 2 arcsin A
7 4 5 6 sylancr A π 2 arcsin A = π 2 arcsin A
8 rere π 2 π 2 = π 2
9 3 8 ax-mp π 2 = π 2
10 9 oveq1i π 2 arcsin A = π 2 arcsin A
11 7 10 eqtrdi A π 2 arcsin A = π 2 arcsin A
12 2 11 eqtrd A arccos A = π 2 arcsin A
13 5 recld A arcsin A
14 resubcl π 2 arcsin A π 2 arcsin A
15 3 13 14 sylancr A π 2 arcsin A
16 asinbnd A arcsin A π 2 π 2
17 neghalfpire π 2
18 17 3 elicc2i arcsin A π 2 π 2 arcsin A π 2 arcsin A arcsin A π 2
19 16 18 sylib A arcsin A π 2 arcsin A arcsin A π 2
20 19 simp3d A arcsin A π 2
21 subge0 π 2 arcsin A 0 π 2 arcsin A arcsin A π 2
22 3 13 21 sylancr A 0 π 2 arcsin A arcsin A π 2
23 20 22 mpbird A 0 π 2 arcsin A
24 3 a1i A π 2
25 pire π
26 25 a1i A π
27 25 recni π
28 17 recni π 2
29 27 4 negsubi π + π 2 = π π 2
30 pidiv2halves π 2 + π 2 = π
31 27 4 4 30 subaddrii π π 2 = π 2
32 29 31 eqtri π + π 2 = π 2
33 4 27 28 32 subaddrii π 2 π = π 2
34 19 simp2d A π 2 arcsin A
35 33 34 eqbrtrid A π 2 π arcsin A
36 24 26 13 35 subled A π 2 arcsin A π
37 0re 0
38 37 25 elicc2i π 2 arcsin A 0 π π 2 arcsin A 0 π 2 arcsin A π 2 arcsin A π
39 15 23 36 38 syl3anbrc A π 2 arcsin A 0 π
40 12 39 eqeltrd A arccos A 0 π