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Mirrors > Home > MPE Home > Th. List > mul2sq | Structured version Visualization version GIF version |
Description: Fibonacci's identity (actually due to Diophantus). The product of two sums of two squares is also a sum of two squares. We can take advantage of Gaussian integers here to trivialize the proof. (Contributed by Mario Carneiro, 19-Jun-2015.) |
Ref | Expression |
---|---|
2sq.1 | ⊢ 𝑆 = ran (𝑤 ∈ ℤ[i] ↦ ((abs‘𝑤)↑2)) |
Ref | Expression |
---|---|
mul2sq | ⊢ ((𝐴 ∈ 𝑆 ∧ 𝐵 ∈ 𝑆) → (𝐴 · 𝐵) ∈ 𝑆) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 2sq.1 | . . 3 ⊢ 𝑆 = ran (𝑤 ∈ ℤ[i] ↦ ((abs‘𝑤)↑2)) | |
2 | 1 | 2sqlem1 27438 | . 2 ⊢ (𝐴 ∈ 𝑆 ↔ ∃𝑥 ∈ ℤ[i] 𝐴 = ((abs‘𝑥)↑2)) |
3 | 1 | 2sqlem1 27438 | . 2 ⊢ (𝐵 ∈ 𝑆 ↔ ∃𝑦 ∈ ℤ[i] 𝐵 = ((abs‘𝑦)↑2)) |
4 | reeanv 3216 | . . 3 ⊢ (∃𝑥 ∈ ℤ[i] ∃𝑦 ∈ ℤ[i] (𝐴 = ((abs‘𝑥)↑2) ∧ 𝐵 = ((abs‘𝑦)↑2)) ↔ (∃𝑥 ∈ ℤ[i] 𝐴 = ((abs‘𝑥)↑2) ∧ ∃𝑦 ∈ ℤ[i] 𝐵 = ((abs‘𝑦)↑2))) | |
5 | gzmulcl 16935 | . . . . . . 7 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → (𝑥 · 𝑦) ∈ ℤ[i]) | |
6 | gzcn 16929 | . . . . . . . . . 10 ⊢ (𝑥 ∈ ℤ[i] → 𝑥 ∈ ℂ) | |
7 | gzcn 16929 | . . . . . . . . . 10 ⊢ (𝑦 ∈ ℤ[i] → 𝑦 ∈ ℂ) | |
8 | absmul 15294 | . . . . . . . . . 10 ⊢ ((𝑥 ∈ ℂ ∧ 𝑦 ∈ ℂ) → (abs‘(𝑥 · 𝑦)) = ((abs‘𝑥) · (abs‘𝑦))) | |
9 | 6, 7, 8 | syl2an 594 | . . . . . . . . 9 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → (abs‘(𝑥 · 𝑦)) = ((abs‘𝑥) · (abs‘𝑦))) |
10 | 9 | oveq1d 7438 | . . . . . . . 8 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → ((abs‘(𝑥 · 𝑦))↑2) = (((abs‘𝑥) · (abs‘𝑦))↑2)) |
11 | 6 | abscld 15436 | . . . . . . . . . 10 ⊢ (𝑥 ∈ ℤ[i] → (abs‘𝑥) ∈ ℝ) |
12 | 11 | recnd 11288 | . . . . . . . . 9 ⊢ (𝑥 ∈ ℤ[i] → (abs‘𝑥) ∈ ℂ) |
13 | 7 | abscld 15436 | . . . . . . . . . 10 ⊢ (𝑦 ∈ ℤ[i] → (abs‘𝑦) ∈ ℝ) |
14 | 13 | recnd 11288 | . . . . . . . . 9 ⊢ (𝑦 ∈ ℤ[i] → (abs‘𝑦) ∈ ℂ) |
15 | sqmul 14133 | . . . . . . . . 9 ⊢ (((abs‘𝑥) ∈ ℂ ∧ (abs‘𝑦) ∈ ℂ) → (((abs‘𝑥) · (abs‘𝑦))↑2) = (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2))) | |
16 | 12, 14, 15 | syl2an 594 | . . . . . . . 8 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → (((abs‘𝑥) · (abs‘𝑦))↑2) = (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2))) |
17 | 10, 16 | eqtr2d 2766 | . . . . . . 7 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) = ((abs‘(𝑥 · 𝑦))↑2)) |
18 | fveq2 6900 | . . . . . . . . 9 ⊢ (𝑧 = (𝑥 · 𝑦) → (abs‘𝑧) = (abs‘(𝑥 · 𝑦))) | |
19 | 18 | oveq1d 7438 | . . . . . . . 8 ⊢ (𝑧 = (𝑥 · 𝑦) → ((abs‘𝑧)↑2) = ((abs‘(𝑥 · 𝑦))↑2)) |
20 | 19 | rspceeqv 3629 | . . . . . . 7 ⊢ (((𝑥 · 𝑦) ∈ ℤ[i] ∧ (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) = ((abs‘(𝑥 · 𝑦))↑2)) → ∃𝑧 ∈ ℤ[i] (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) = ((abs‘𝑧)↑2)) |
21 | 5, 17, 20 | syl2anc 582 | . . . . . 6 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → ∃𝑧 ∈ ℤ[i] (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) = ((abs‘𝑧)↑2)) |
22 | 1 | 2sqlem1 27438 | . . . . . 6 ⊢ ((((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) ∈ 𝑆 ↔ ∃𝑧 ∈ ℤ[i] (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) = ((abs‘𝑧)↑2)) |
23 | 21, 22 | sylibr 233 | . . . . 5 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) ∈ 𝑆) |
24 | oveq12 7432 | . . . . . 6 ⊢ ((𝐴 = ((abs‘𝑥)↑2) ∧ 𝐵 = ((abs‘𝑦)↑2)) → (𝐴 · 𝐵) = (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2))) | |
25 | 24 | eleq1d 2810 | . . . . 5 ⊢ ((𝐴 = ((abs‘𝑥)↑2) ∧ 𝐵 = ((abs‘𝑦)↑2)) → ((𝐴 · 𝐵) ∈ 𝑆 ↔ (((abs‘𝑥)↑2) · ((abs‘𝑦)↑2)) ∈ 𝑆)) |
26 | 23, 25 | syl5ibrcom 246 | . . . 4 ⊢ ((𝑥 ∈ ℤ[i] ∧ 𝑦 ∈ ℤ[i]) → ((𝐴 = ((abs‘𝑥)↑2) ∧ 𝐵 = ((abs‘𝑦)↑2)) → (𝐴 · 𝐵) ∈ 𝑆)) |
27 | 26 | rexlimivv 3189 | . . 3 ⊢ (∃𝑥 ∈ ℤ[i] ∃𝑦 ∈ ℤ[i] (𝐴 = ((abs‘𝑥)↑2) ∧ 𝐵 = ((abs‘𝑦)↑2)) → (𝐴 · 𝐵) ∈ 𝑆) |
28 | 4, 27 | sylbir 234 | . 2 ⊢ ((∃𝑥 ∈ ℤ[i] 𝐴 = ((abs‘𝑥)↑2) ∧ ∃𝑦 ∈ ℤ[i] 𝐵 = ((abs‘𝑦)↑2)) → (𝐴 · 𝐵) ∈ 𝑆) |
29 | 2, 3, 28 | syl2anb 596 | 1 ⊢ ((𝐴 ∈ 𝑆 ∧ 𝐵 ∈ 𝑆) → (𝐴 · 𝐵) ∈ 𝑆) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 394 = wceq 1533 ∈ wcel 2098 ∃wrex 3059 ↦ cmpt 5235 ran crn 5682 ‘cfv 6553 (class class class)co 7423 ℂcc 11152 · cmul 11159 2c2 12314 ↑cexp 14076 abscabs 15234 ℤ[i]cgz 16926 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1789 ax-4 1803 ax-5 1905 ax-6 1963 ax-7 2003 ax-8 2100 ax-9 2108 ax-10 2129 ax-11 2146 ax-12 2166 ax-ext 2696 ax-sep 5303 ax-nul 5310 ax-pow 5368 ax-pr 5432 ax-un 7745 ax-cnex 11210 ax-resscn 11211 ax-1cn 11212 ax-icn 11213 ax-addcl 11214 ax-addrcl 11215 ax-mulcl 11216 ax-mulrcl 11217 ax-mulcom 11218 ax-addass 11219 ax-mulass 11220 ax-distr 11221 ax-i2m1 11222 ax-1ne0 11223 ax-1rid 11224 ax-rnegex 11225 ax-rrecex 11226 ax-cnre 11227 ax-pre-lttri 11228 ax-pre-lttrn 11229 ax-pre-ltadd 11230 ax-pre-mulgt0 11231 ax-pre-sup 11232 |
This theorem depends on definitions: df-bi 206 df-an 395 df-or 846 df-3or 1085 df-3an 1086 df-tru 1536 df-fal 1546 df-ex 1774 df-nf 1778 df-sb 2060 df-mo 2528 df-eu 2557 df-clab 2703 df-cleq 2717 df-clel 2802 df-nfc 2877 df-ne 2930 df-nel 3036 df-ral 3051 df-rex 3060 df-rmo 3363 df-reu 3364 df-rab 3419 df-v 3463 df-sbc 3776 df-csb 3892 df-dif 3949 df-un 3951 df-in 3953 df-ss 3963 df-pss 3966 df-nul 4325 df-if 4533 df-pw 4608 df-sn 4633 df-pr 4635 df-op 4639 df-uni 4913 df-iun 5002 df-br 5153 df-opab 5215 df-mpt 5236 df-tr 5270 df-id 5579 df-eprel 5585 df-po 5593 df-so 5594 df-fr 5636 df-we 5638 df-xp 5687 df-rel 5688 df-cnv 5689 df-co 5690 df-dm 5691 df-rn 5692 df-res 5693 df-ima 5694 df-pred 6311 df-ord 6378 df-on 6379 df-lim 6380 df-suc 6381 df-iota 6505 df-fun 6555 df-fn 6556 df-f 6557 df-f1 6558 df-fo 6559 df-f1o 6560 df-fv 6561 df-riota 7379 df-ov 7426 df-oprab 7427 df-mpo 7428 df-om 7876 df-2nd 8003 df-frecs 8295 df-wrecs 8326 df-recs 8400 df-rdg 8439 df-er 8733 df-en 8974 df-dom 8975 df-sdom 8976 df-sup 9481 df-pnf 11296 df-mnf 11297 df-xr 11298 df-ltxr 11299 df-le 11300 df-sub 11492 df-neg 11493 df-div 11918 df-nn 12260 df-2 12322 df-3 12323 df-n0 12520 df-z 12606 df-uz 12870 df-rp 13024 df-seq 14017 df-exp 14077 df-cj 15099 df-re 15100 df-im 15101 df-sqrt 15235 df-abs 15236 df-gz 16927 |
This theorem is referenced by: (None) |
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