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Mirrors > Home > ILE Home > Th. List > faclbnd2 | GIF version |
Description: A lower bound for the factorial function. (Contributed by NM, 17-Dec-2005.) |
Ref | Expression |
---|---|
faclbnd2 | ⊢ (𝑁 ∈ ℕ0 → ((2↑𝑁) / 2) ≤ (!‘𝑁)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sq2 10388 | . . . . . 6 ⊢ (2↑2) = 4 | |
2 | 2t2e4 8874 | . . . . . 6 ⊢ (2 · 2) = 4 | |
3 | 1, 2 | eqtr4i 2163 | . . . . 5 ⊢ (2↑2) = (2 · 2) |
4 | 3 | oveq2i 5785 | . . . 4 ⊢ ((2↑(𝑁 + 1)) / (2↑2)) = ((2↑(𝑁 + 1)) / (2 · 2)) |
5 | 2cn 8791 | . . . . . 6 ⊢ 2 ∈ ℂ | |
6 | expp1 10300 | . . . . . 6 ⊢ ((2 ∈ ℂ ∧ 𝑁 ∈ ℕ0) → (2↑(𝑁 + 1)) = ((2↑𝑁) · 2)) | |
7 | 5, 6 | mpan 420 | . . . . 5 ⊢ (𝑁 ∈ ℕ0 → (2↑(𝑁 + 1)) = ((2↑𝑁) · 2)) |
8 | 7 | oveq1d 5789 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → ((2↑(𝑁 + 1)) / (2 · 2)) = (((2↑𝑁) · 2) / (2 · 2))) |
9 | 4, 8 | syl5eq 2184 | . . 3 ⊢ (𝑁 ∈ ℕ0 → ((2↑(𝑁 + 1)) / (2↑2)) = (((2↑𝑁) · 2) / (2 · 2))) |
10 | expcl 10311 | . . . . 5 ⊢ ((2 ∈ ℂ ∧ 𝑁 ∈ ℕ0) → (2↑𝑁) ∈ ℂ) | |
11 | 5, 10 | mpan 420 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → (2↑𝑁) ∈ ℂ) |
12 | 5 | a1i 9 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → 2 ∈ ℂ) |
13 | 2ap0 8813 | . . . . 5 ⊢ 2 # 0 | |
14 | 13 | a1i 9 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → 2 # 0) |
15 | 11, 12, 12, 12, 14, 14 | divmuldivapd 8592 | . . 3 ⊢ (𝑁 ∈ ℕ0 → (((2↑𝑁) / 2) · (2 / 2)) = (((2↑𝑁) · 2) / (2 · 2))) |
16 | 2div2e1 8852 | . . . . 5 ⊢ (2 / 2) = 1 | |
17 | 16 | oveq2i 5785 | . . . 4 ⊢ (((2↑𝑁) / 2) · (2 / 2)) = (((2↑𝑁) / 2) · 1) |
18 | 11 | halfcld 8964 | . . . . 5 ⊢ (𝑁 ∈ ℕ0 → ((2↑𝑁) / 2) ∈ ℂ) |
19 | 18 | mulid1d 7783 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → (((2↑𝑁) / 2) · 1) = ((2↑𝑁) / 2)) |
20 | 17, 19 | syl5eq 2184 | . . 3 ⊢ (𝑁 ∈ ℕ0 → (((2↑𝑁) / 2) · (2 / 2)) = ((2↑𝑁) / 2)) |
21 | 9, 15, 20 | 3eqtr2rd 2179 | . 2 ⊢ (𝑁 ∈ ℕ0 → ((2↑𝑁) / 2) = ((2↑(𝑁 + 1)) / (2↑2))) |
22 | 2nn0 8994 | . . . 4 ⊢ 2 ∈ ℕ0 | |
23 | faclbnd 10487 | . . . 4 ⊢ ((2 ∈ ℕ0 ∧ 𝑁 ∈ ℕ0) → (2↑(𝑁 + 1)) ≤ ((2↑2) · (!‘𝑁))) | |
24 | 22, 23 | mpan 420 | . . 3 ⊢ (𝑁 ∈ ℕ0 → (2↑(𝑁 + 1)) ≤ ((2↑2) · (!‘𝑁))) |
25 | 2re 8790 | . . . . 5 ⊢ 2 ∈ ℝ | |
26 | peano2nn0 9017 | . . . . 5 ⊢ (𝑁 ∈ ℕ0 → (𝑁 + 1) ∈ ℕ0) | |
27 | reexpcl 10310 | . . . . 5 ⊢ ((2 ∈ ℝ ∧ (𝑁 + 1) ∈ ℕ0) → (2↑(𝑁 + 1)) ∈ ℝ) | |
28 | 25, 26, 27 | sylancr 410 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → (2↑(𝑁 + 1)) ∈ ℝ) |
29 | faccl 10481 | . . . . 5 ⊢ (𝑁 ∈ ℕ0 → (!‘𝑁) ∈ ℕ) | |
30 | 29 | nnred 8733 | . . . 4 ⊢ (𝑁 ∈ ℕ0 → (!‘𝑁) ∈ ℝ) |
31 | 4re 8797 | . . . . . . 7 ⊢ 4 ∈ ℝ | |
32 | 1, 31 | eqeltri 2212 | . . . . . 6 ⊢ (2↑2) ∈ ℝ |
33 | 4pos 8817 | . . . . . . 7 ⊢ 0 < 4 | |
34 | 33, 1 | breqtrri 3955 | . . . . . 6 ⊢ 0 < (2↑2) |
35 | 32, 34 | pm3.2i 270 | . . . . 5 ⊢ ((2↑2) ∈ ℝ ∧ 0 < (2↑2)) |
36 | ledivmul 8635 | . . . . 5 ⊢ (((2↑(𝑁 + 1)) ∈ ℝ ∧ (!‘𝑁) ∈ ℝ ∧ ((2↑2) ∈ ℝ ∧ 0 < (2↑2))) → (((2↑(𝑁 + 1)) / (2↑2)) ≤ (!‘𝑁) ↔ (2↑(𝑁 + 1)) ≤ ((2↑2) · (!‘𝑁)))) | |
37 | 35, 36 | mp3an3 1304 | . . . 4 ⊢ (((2↑(𝑁 + 1)) ∈ ℝ ∧ (!‘𝑁) ∈ ℝ) → (((2↑(𝑁 + 1)) / (2↑2)) ≤ (!‘𝑁) ↔ (2↑(𝑁 + 1)) ≤ ((2↑2) · (!‘𝑁)))) |
38 | 28, 30, 37 | syl2anc 408 | . . 3 ⊢ (𝑁 ∈ ℕ0 → (((2↑(𝑁 + 1)) / (2↑2)) ≤ (!‘𝑁) ↔ (2↑(𝑁 + 1)) ≤ ((2↑2) · (!‘𝑁)))) |
39 | 24, 38 | mpbird 166 | . 2 ⊢ (𝑁 ∈ ℕ0 → ((2↑(𝑁 + 1)) / (2↑2)) ≤ (!‘𝑁)) |
40 | 21, 39 | eqbrtrd 3950 | 1 ⊢ (𝑁 ∈ ℕ0 → ((2↑𝑁) / 2) ≤ (!‘𝑁)) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 103 ↔ wb 104 = wceq 1331 ∈ wcel 1480 class class class wbr 3929 ‘cfv 5123 (class class class)co 5774 ℂcc 7618 ℝcr 7619 0cc0 7620 1c1 7621 + caddc 7623 · cmul 7625 < clt 7800 ≤ cle 7801 # cap 8343 / cdiv 8432 2c2 8771 4c4 8773 ℕ0cn0 8977 ↑cexp 10292 !cfa 10471 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 ax-in1 603 ax-in2 604 ax-io 698 ax-5 1423 ax-7 1424 ax-gen 1425 ax-ie1 1469 ax-ie2 1470 ax-8 1482 ax-10 1483 ax-11 1484 ax-i12 1485 ax-bndl 1486 ax-4 1487 ax-13 1491 ax-14 1492 ax-17 1506 ax-i9 1510 ax-ial 1514 ax-i5r 1515 ax-ext 2121 ax-coll 4043 ax-sep 4046 ax-nul 4054 ax-pow 4098 ax-pr 4131 ax-un 4355 ax-setind 4452 ax-iinf 4502 ax-cnex 7711 ax-resscn 7712 ax-1cn 7713 ax-1re 7714 ax-icn 7715 ax-addcl 7716 ax-addrcl 7717 ax-mulcl 7718 ax-mulrcl 7719 ax-addcom 7720 ax-mulcom 7721 ax-addass 7722 ax-mulass 7723 ax-distr 7724 ax-i2m1 7725 ax-0lt1 7726 ax-1rid 7727 ax-0id 7728 ax-rnegex 7729 ax-precex 7730 ax-cnre 7731 ax-pre-ltirr 7732 ax-pre-ltwlin 7733 ax-pre-lttrn 7734 ax-pre-apti 7735 ax-pre-ltadd 7736 ax-pre-mulgt0 7737 ax-pre-mulext 7738 |
This theorem depends on definitions: df-bi 116 df-dc 820 df-3or 963 df-3an 964 df-tru 1334 df-fal 1337 df-nf 1437 df-sb 1736 df-eu 2002 df-mo 2003 df-clab 2126 df-cleq 2132 df-clel 2135 df-nfc 2270 df-ne 2309 df-nel 2404 df-ral 2421 df-rex 2422 df-reu 2423 df-rmo 2424 df-rab 2425 df-v 2688 df-sbc 2910 df-csb 3004 df-dif 3073 df-un 3075 df-in 3077 df-ss 3084 df-nul 3364 df-if 3475 df-pw 3512 df-sn 3533 df-pr 3534 df-op 3536 df-uni 3737 df-int 3772 df-iun 3815 df-br 3930 df-opab 3990 df-mpt 3991 df-tr 4027 df-id 4215 df-po 4218 df-iso 4219 df-iord 4288 df-on 4290 df-ilim 4291 df-suc 4293 df-iom 4505 df-xp 4545 df-rel 4546 df-cnv 4547 df-co 4548 df-dm 4549 df-rn 4550 df-res 4551 df-ima 4552 df-iota 5088 df-fun 5125 df-fn 5126 df-f 5127 df-f1 5128 df-fo 5129 df-f1o 5130 df-fv 5131 df-riota 5730 df-ov 5777 df-oprab 5778 df-mpo 5779 df-1st 6038 df-2nd 6039 df-recs 6202 df-frec 6288 df-pnf 7802 df-mnf 7803 df-xr 7804 df-ltxr 7805 df-le 7806 df-sub 7935 df-neg 7936 df-reap 8337 df-ap 8344 df-div 8433 df-inn 8721 df-2 8779 df-3 8780 df-4 8781 df-n0 8978 df-z 9055 df-uz 9327 df-rp 9442 df-seqfrec 10219 df-exp 10293 df-fac 10472 |
This theorem is referenced by: ege2le3 11377 |
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