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Theorem cphpyth 25262

Description: The pythagorean theorem for a subcomplex pre-Hilbert space. The square of the norm of the sum of two orthogonal vectors (i.e., whose inner product is 0) is the sum of the squares of their norms. Problem 2 in [Kreyszig] p. 135. This is Metamath 100 proof #4. (Contributed by NM, 17-Apr-2008.) (Revised by SN, 22-Sep-2024.)

**Hypotheses**
Ref	Expression
cphpyth.v	⊢ 𝑉 = (Base‘𝑊)
cphpyth.h	⊢ , = (·_𝑖‘𝑊)
cphpyth.p	⊢ + = (+_g‘𝑊)
cphpyth.n	⊢ 𝑁 = (norm‘𝑊)
cphpyth.w	⊢ (𝜑 → 𝑊 ∈ ℂPreHil)
cphpyth.a	⊢ (𝜑 → 𝐴 ∈ 𝑉)
cphpyth.b	⊢ (𝜑 → 𝐵 ∈ 𝑉)

**Assertion**
Ref	Expression
cphpyth	⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝑁‘(𝐴 + 𝐵))↑2) = (((𝑁‘𝐴)↑2) + ((𝑁‘𝐵)↑2)))

**Proof of Theorem cphpyth**
Step	Hyp	Ref	Expression
1		cphpyth.h	. . . . 5 ⊢ , = (·_𝑖‘𝑊)
2		cphpyth.v	. . . . 5 ⊢ 𝑉 = (Base‘𝑊)
3		cphpyth.p	. . . . 5 ⊢ + = (+_g‘𝑊)
4		cphpyth.w	. . . . 5 ⊢ (𝜑 → 𝑊 ∈ ℂPreHil)
5		cphpyth.a	. . . . 5 ⊢ (𝜑 → 𝐴 ∈ 𝑉)
6		cphpyth.b	. . . . 5 ⊢ (𝜑 → 𝐵 ∈ 𝑉)
7	1, 2, 3, 4, 5, 6, 5, 6	cph2di 25253	. . . 4 ⊢ (𝜑 → ((𝐴 + 𝐵) , (𝐴 + 𝐵)) = (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + ((𝐴 , 𝐵) + (𝐵 , 𝐴))))
8	7	adantr 480	. . 3 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝐴 + 𝐵) , (𝐴 + 𝐵)) = (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + ((𝐴 , 𝐵) + (𝐵 , 𝐴))))
9		simpr 484	. . . . . 6 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → (𝐴 , 𝐵) = 0)
10	1, 2	cphorthcom 25247	. . . . . . . 8 ⊢ ((𝑊 ∈ ℂPreHil ∧ 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉) → ((𝐴 , 𝐵) = 0 ↔ (𝐵 , 𝐴) = 0))
11	4, 5, 6, 10	syl3anc 1371	. . . . . . 7 ⊢ (𝜑 → ((𝐴 , 𝐵) = 0 ↔ (𝐵 , 𝐴) = 0))
12	11	biimpa 476	. . . . . 6 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → (𝐵 , 𝐴) = 0)
13	9, 12	oveq12d 7463	. . . . 5 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝐴 , 𝐵) + (𝐵 , 𝐴)) = (0 + 0))
14		00id 11461	. . . . 5 ⊢ (0 + 0) = 0
15	13, 14	eqtrdi 2790	. . . 4 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝐴 , 𝐵) + (𝐵 , 𝐴)) = 0)
16	15	oveq2d 7461	. . 3 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + ((𝐴 , 𝐵) + (𝐵 , 𝐴))) = (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + 0))
17	2, 1	cphipcl 25237	. . . . . . 7 ⊢ ((𝑊 ∈ ℂPreHil ∧ 𝐴 ∈ 𝑉 ∧ 𝐴 ∈ 𝑉) → (𝐴 , 𝐴) ∈ ℂ)
18	4, 5, 5, 17	syl3anc 1371	. . . . . 6 ⊢ (𝜑 → (𝐴 , 𝐴) ∈ ℂ)
19	2, 1	cphipcl 25237	. . . . . . 7 ⊢ ((𝑊 ∈ ℂPreHil ∧ 𝐵 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉) → (𝐵 , 𝐵) ∈ ℂ)
20	4, 6, 6, 19	syl3anc 1371	. . . . . 6 ⊢ (𝜑 → (𝐵 , 𝐵) ∈ ℂ)
21	18, 20	addcld 11305	. . . . 5 ⊢ (𝜑 → ((𝐴 , 𝐴) + (𝐵 , 𝐵)) ∈ ℂ)
22	21	addridd 11486	. . . 4 ⊢ (𝜑 → (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + 0) = ((𝐴 , 𝐴) + (𝐵 , 𝐵)))
23	22	adantr 480	. . 3 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → (((𝐴 , 𝐴) + (𝐵 , 𝐵)) + 0) = ((𝐴 , 𝐴) + (𝐵 , 𝐵)))
24	8, 16, 23	3eqtrd 2778	. 2 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝐴 + 𝐵) , (𝐴 + 𝐵)) = ((𝐴 , 𝐴) + (𝐵 , 𝐵)))
25		cphngp 25219	. . . . . 6 ⊢ (𝑊 ∈ ℂPreHil → 𝑊 ∈ NrmGrp)
26		ngpgrp 24626	. . . . . 6 ⊢ (𝑊 ∈ NrmGrp → 𝑊 ∈ Grp)
27	4, 25, 26	3syl 18	. . . . 5 ⊢ (𝜑 → 𝑊 ∈ Grp)
28	2, 3, 27, 5, 6	grpcld 18982	. . . 4 ⊢ (𝜑 → (𝐴 + 𝐵) ∈ 𝑉)
29		cphpyth.n	. . . . 5 ⊢ 𝑁 = (norm‘𝑊)
30	2, 1, 29	nmsq 25240	. . . 4 ⊢ ((𝑊 ∈ ℂPreHil ∧ (𝐴 + 𝐵) ∈ 𝑉) → ((𝑁‘(𝐴 + 𝐵))↑2) = ((𝐴 + 𝐵) , (𝐴 + 𝐵)))
31	4, 28, 30	syl2anc 583	. . 3 ⊢ (𝜑 → ((𝑁‘(𝐴 + 𝐵))↑2) = ((𝐴 + 𝐵) , (𝐴 + 𝐵)))
32	31	adantr 480	. 2 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝑁‘(𝐴 + 𝐵))↑2) = ((𝐴 + 𝐵) , (𝐴 + 𝐵)))
33	2, 1, 29	nmsq 25240	. . . . 5 ⊢ ((𝑊 ∈ ℂPreHil ∧ 𝐴 ∈ 𝑉) → ((𝑁‘𝐴)↑2) = (𝐴 , 𝐴))
34	4, 5, 33	syl2anc 583	. . . 4 ⊢ (𝜑 → ((𝑁‘𝐴)↑2) = (𝐴 , 𝐴))
35	2, 1, 29	nmsq 25240	. . . . 5 ⊢ ((𝑊 ∈ ℂPreHil ∧ 𝐵 ∈ 𝑉) → ((𝑁‘𝐵)↑2) = (𝐵 , 𝐵))
36	4, 6, 35	syl2anc 583	. . . 4 ⊢ (𝜑 → ((𝑁‘𝐵)↑2) = (𝐵 , 𝐵))
37	34, 36	oveq12d 7463	. . 3 ⊢ (𝜑 → (((𝑁‘𝐴)↑2) + ((𝑁‘𝐵)↑2)) = ((𝐴 , 𝐴) + (𝐵 , 𝐵)))
38	37	adantr 480	. 2 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → (((𝑁‘𝐴)↑2) + ((𝑁‘𝐵)↑2)) = ((𝐴 , 𝐴) + (𝐵 , 𝐵)))
39	24, 32, 38	3eqtr4d 2784	1 ⊢ ((𝜑 ∧ (𝐴 , 𝐵) = 0) → ((𝑁‘(𝐴 + 𝐵))↑2) = (((𝑁‘𝐴)↑2) + ((𝑁‘𝐵)↑2)))

Colors of variables: wff setvar class

Syntax hints: → wi 4 ↔ wb 206 ∧ wa 395 = wceq 1537 ∈ wcel 2103 ‘cfv 6572 (class class class)co 7445 ℂcc 11178 0cc0 11180 + caddc 11183 2c2 12344 ↑cexp 14108 Basecbs 17253 +_gcplusg 17306 ·_𝑖cip 17311 Grpcgrp 18968 normcnm 24603 NrmGrpcngp 24604 ℂPreHilccph 25212

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1793 ax-4 1807 ax-5 1909 ax-6 1967 ax-7 2007 ax-8 2105 ax-9 2113 ax-10 2136 ax-11 2153 ax-12 2173 ax-ext 2705 ax-rep 5306 ax-sep 5320 ax-nul 5327 ax-pow 5386 ax-pr 5450 ax-un 7766 ax-cnex 11236 ax-resscn 11237 ax-1cn 11238 ax-icn 11239 ax-addcl 11240 ax-addrcl 11241 ax-mulcl 11242 ax-mulrcl 11243 ax-mulcom 11244 ax-addass 11245 ax-mulass 11246 ax-distr 11247 ax-i2m1 11248 ax-1ne0 11249 ax-1rid 11250 ax-rnegex 11251 ax-rrecex 11252 ax-cnre 11253 ax-pre-lttri 11254 ax-pre-lttrn 11255 ax-pre-ltadd 11256 ax-pre-mulgt0 11257 ax-pre-sup 11258 ax-addf 11259 ax-mulf 11260

This theorem depends on definitions: df-bi 207 df-an 396 df-or 847 df-3or 1088 df-3an 1089 df-tru 1540 df-fal 1550 df-ex 1778 df-nf 1782 df-sb 2065 df-mo 2537 df-eu 2566 df-clab 2712 df-cleq 2726 df-clel 2813 df-nfc 2890 df-ne 2943 df-nel 3049 df-ral 3064 df-rex 3073 df-rmo 3383 df-reu 3384 df-rab 3439 df-v 3484 df-sbc 3799 df-csb 3916 df-dif 3973 df-un 3975 df-in 3977 df-ss 3987 df-pss 3990 df-nul 4348 df-if 4549 df-pw 4624 df-sn 4649 df-pr 4651 df-tp 4653 df-op 4655 df-uni 4932 df-iun 5021 df-br 5170 df-opab 5232 df-mpt 5253 df-tr 5287 df-id 5597 df-eprel 5603 df-po 5611 df-so 5612 df-fr 5654 df-we 5656 df-xp 5705 df-rel 5706 df-cnv 5707 df-co 5708 df-dm 5709 df-rn 5710 df-res 5711 df-ima 5712 df-pred 6331 df-ord 6397 df-on 6398 df-lim 6399 df-suc 6400 df-iota 6524 df-fun 6574 df-fn 6575 df-f 6576 df-f1 6577 df-fo 6578 df-f1o 6579 df-fv 6580 df-riota 7401 df-ov 7448 df-oprab 7449 df-mpo 7450 df-om 7900 df-1st 8026 df-2nd 8027 df-tpos 8263 df-frecs 8318 df-wrecs 8349 df-recs 8423 df-rdg 8462 df-1o 8518 df-er 8759 df-map 8882 df-en 9000 df-dom 9001 df-sdom 9002 df-fin 9003 df-sup 9507 df-pnf 11322 df-mnf 11323 df-xr 11324 df-ltxr 11325 df-le 11326 df-sub 11518 df-neg 11519 df-div 11944 df-nn 12290 df-2 12352 df-3 12353 df-4 12354 df-5 12355 df-6 12356 df-7 12357 df-8 12358 df-9 12359 df-n0 12550 df-z 12636 df-dec 12755 df-uz 12900 df-rp 13054 df-fz 13564 df-seq 14049 df-exp 14109 df-cj 15144 df-re 15145 df-im 15146 df-sqrt 15280 df-abs 15281 df-struct 17189 df-sets 17206 df-slot 17224 df-ndx 17236 df-base 17254 df-ress 17283 df-plusg 17319 df-mulr 17320 df-starv 17321 df-sca 17322 df-vsca 17323 df-ip 17324 df-tset 17325 df-ple 17326 df-ds 17328 df-unif 17329 df-0g 17496 df-mgm 18673 df-sgrp 18752 df-mnd 18768 df-mhm 18813 df-grp 18971 df-minusg 18972 df-subg 19158 df-ghm 19248 df-cmn 19819 df-abl 19820 df-mgp 20157 df-rng 20175 df-ur 20204 df-ring 20257 df-cring 20258 df-oppr 20355 df-dvdsr 20378 df-unit 20379 df-rhm 20493 df-subrg 20592 df-drng 20748 df-staf 20857 df-srng 20858 df-lmod 20877 df-lmhm 21039 df-lvec 21120 df-sra 21190 df-rgmod 21191 df-cnfld 21383 df-phl 21662 df-ngp 24610 df-nlm 24613 df-clm 25108 df-cph 25214

This theorem is referenced by: (None)

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