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Theorem faclbnd2 11320
Description: A lower bound for the factorial function. (Contributed by NM, 17-Dec-2005.)
Assertion
Ref Expression
faclbnd2  |-  ( N  e.  NN0  ->  ( ( 2 ^ N )  /  2 )  <_ 
( ! `  N
) )

Proof of Theorem faclbnd2
StepHypRef Expression
1 sq2 11215 . . . . . 6  |-  ( 2 ^ 2 )  =  4
2 2t2e4 9887 . . . . . 6  |-  ( 2  x.  2 )  =  4
31, 2eqtr4i 2319 . . . . 5  |-  ( 2 ^ 2 )  =  ( 2  x.  2 )
43oveq2i 5885 . . . 4  |-  ( ( 2 ^ ( N  +  1 ) )  /  ( 2 ^ 2 ) )  =  ( ( 2 ^ ( N  +  1 ) )  /  (
2  x.  2 ) )
5 2cn 9832 . . . . . 6  |-  2  e.  CC
6 expp1 11126 . . . . . 6  |-  ( ( 2  e.  CC  /\  N  e.  NN0 )  -> 
( 2 ^ ( N  +  1 ) )  =  ( ( 2 ^ N )  x.  2 ) )
75, 6mpan 651 . . . . 5  |-  ( N  e.  NN0  ->  ( 2 ^ ( N  + 
1 ) )  =  ( ( 2 ^ N )  x.  2 ) )
87oveq1d 5889 . . . 4  |-  ( N  e.  NN0  ->  ( ( 2 ^ ( N  +  1 ) )  /  ( 2  x.  2 ) )  =  ( ( ( 2 ^ N )  x.  2 )  /  (
2  x.  2 ) ) )
94, 8syl5eq 2340 . . 3  |-  ( N  e.  NN0  ->  ( ( 2 ^ ( N  +  1 ) )  /  ( 2 ^ 2 ) )  =  ( ( ( 2 ^ N )  x.  2 )  /  (
2  x.  2 ) ) )
10 expcl 11137 . . . . 5  |-  ( ( 2  e.  CC  /\  N  e.  NN0 )  -> 
( 2 ^ N
)  e.  CC )
115, 10mpan 651 . . . 4  |-  ( N  e.  NN0  ->  ( 2 ^ N )  e.  CC )
12 2ne0 9845 . . . . . 6  |-  2  =/=  0
135, 12pm3.2i 441 . . . . 5  |-  ( 2  e.  CC  /\  2  =/=  0 )
14 divmuldiv 9476 . . . . 5  |-  ( ( ( ( 2 ^ N )  e.  CC  /\  2  e.  CC )  /\  ( ( 2  e.  CC  /\  2  =/=  0 )  /\  (
2  e.  CC  /\  2  =/=  0 ) ) )  ->  ( (
( 2 ^ N
)  /  2 )  x.  ( 2  / 
2 ) )  =  ( ( ( 2 ^ N )  x.  2 )  /  (
2  x.  2 ) ) )
1513, 13, 14mpanr12 666 . . . 4  |-  ( ( ( 2 ^ N
)  e.  CC  /\  2  e.  CC )  ->  ( ( ( 2 ^ N )  / 
2 )  x.  (
2  /  2 ) )  =  ( ( ( 2 ^ N
)  x.  2 )  /  ( 2  x.  2 ) ) )
1611, 5, 15sylancl 643 . . 3  |-  ( N  e.  NN0  ->  ( ( ( 2 ^ N
)  /  2 )  x.  ( 2  / 
2 ) )  =  ( ( ( 2 ^ N )  x.  2 )  /  (
2  x.  2 ) ) )
175, 12dividi 9509 . . . . 5  |-  ( 2  /  2 )  =  1
1817oveq2i 5885 . . . 4  |-  ( ( ( 2 ^ N
)  /  2 )  x.  ( 2  / 
2 ) )  =  ( ( ( 2 ^ N )  / 
2 )  x.  1 )
1911halfcld 9972 . . . . 5  |-  ( N  e.  NN0  ->  ( ( 2 ^ N )  /  2 )  e.  CC )
2019mulid1d 8868 . . . 4  |-  ( N  e.  NN0  ->  ( ( ( 2 ^ N
)  /  2 )  x.  1 )  =  ( ( 2 ^ N )  /  2
) )
2118, 20syl5eq 2340 . . 3  |-  ( N  e.  NN0  ->  ( ( ( 2 ^ N
)  /  2 )  x.  ( 2  / 
2 ) )  =  ( ( 2 ^ N )  /  2
) )
229, 16, 213eqtr2rd 2335 . 2  |-  ( N  e.  NN0  ->  ( ( 2 ^ N )  /  2 )  =  ( ( 2 ^ ( N  +  1 ) )  /  (
2 ^ 2 ) ) )
23 2nn0 9998 . . . 4  |-  2  e.  NN0
24 faclbnd 11319 . . . 4  |-  ( ( 2  e.  NN0  /\  N  e.  NN0 )  -> 
( 2 ^ ( N  +  1 ) )  <_  ( (
2 ^ 2 )  x.  ( ! `  N ) ) )
2523, 24mpan 651 . . 3  |-  ( N  e.  NN0  ->  ( 2 ^ ( N  + 
1 ) )  <_ 
( ( 2 ^ 2 )  x.  ( ! `  N )
) )
26 2re 9831 . . . . 5  |-  2  e.  RR
27 peano2nn0 10020 . . . . 5  |-  ( N  e.  NN0  ->  ( N  +  1 )  e. 
NN0 )
28 reexpcl 11136 . . . . 5  |-  ( ( 2  e.  RR  /\  ( N  +  1
)  e.  NN0 )  ->  ( 2 ^ ( N  +  1 ) )  e.  RR )
2926, 27, 28sylancr 644 . . . 4  |-  ( N  e.  NN0  ->  ( 2 ^ ( N  + 
1 ) )  e.  RR )
30 faccl 11314 . . . . 5  |-  ( N  e.  NN0  ->  ( ! `
 N )  e.  NN )
3130nnred 9777 . . . 4  |-  ( N  e.  NN0  ->  ( ! `
 N )  e.  RR )
32 4re 9835 . . . . . . 7  |-  4  e.  RR
331, 32eqeltri 2366 . . . . . 6  |-  ( 2 ^ 2 )  e.  RR
34 4pos 9848 . . . . . . 7  |-  0  <  4
3534, 1breqtrri 4064 . . . . . 6  |-  0  <  ( 2 ^ 2 )
3633, 35pm3.2i 441 . . . . 5  |-  ( ( 2 ^ 2 )  e.  RR  /\  0  <  ( 2 ^ 2 ) )
37 ledivmul 9645 . . . . 5  |-  ( ( ( 2 ^ ( N  +  1 ) )  e.  RR  /\  ( ! `  N )  e.  RR  /\  (
( 2 ^ 2 )  e.  RR  /\  0  <  ( 2 ^ 2 ) ) )  ->  ( ( ( 2 ^ ( N  +  1 ) )  /  ( 2 ^ 2 ) )  <_ 
( ! `  N
)  <->  ( 2 ^ ( N  +  1 ) )  <_  (
( 2 ^ 2 )  x.  ( ! `
 N ) ) ) )
3836, 37mp3an3 1266 . . . 4  |-  ( ( ( 2 ^ ( N  +  1 ) )  e.  RR  /\  ( ! `  N )  e.  RR )  -> 
( ( ( 2 ^ ( N  + 
1 ) )  / 
( 2 ^ 2 ) )  <_  ( ! `  N )  <->  ( 2 ^ ( N  +  1 ) )  <_  ( ( 2 ^ 2 )  x.  ( ! `  N
) ) ) )
3929, 31, 38syl2anc 642 . . 3  |-  ( N  e.  NN0  ->  ( ( ( 2 ^ ( N  +  1 ) )  /  ( 2 ^ 2 ) )  <_  ( ! `  N )  <->  ( 2 ^ ( N  + 
1 ) )  <_ 
( ( 2 ^ 2 )  x.  ( ! `  N )
) ) )
4025, 39mpbird 223 . 2  |-  ( N  e.  NN0  ->  ( ( 2 ^ ( N  +  1 ) )  /  ( 2 ^ 2 ) )  <_ 
( ! `  N
) )
4122, 40eqbrtrd 4059 1  |-  ( N  e.  NN0  ->  ( ( 2 ^ N )  /  2 )  <_ 
( ! `  N
) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 176    /\ wa 358    = wceq 1632    e. wcel 1696    =/= wne 2459   class class class wbr 4039   ` cfv 5271  (class class class)co 5874   CCcc 8751   RRcr 8752   0cc0 8753   1c1 8754    + caddc 8756    x. cmul 8758    < clt 8883    <_ cle 8884    / cdiv 9439   2c2 9811   4c4 9813   NN0cn0 9981   ^cexp 11120   !cfa 11304
This theorem is referenced by:  ege2le3  12387
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1536  ax-5 1547  ax-17 1606  ax-9 1644  ax-8 1661  ax-13 1698  ax-14 1700  ax-6 1715  ax-7 1720  ax-11 1727  ax-12 1878  ax-ext 2277  ax-sep 4157  ax-nul 4165  ax-pow 4204  ax-pr 4230  ax-un 4528  ax-cnex 8809  ax-resscn 8810  ax-1cn 8811  ax-icn 8812  ax-addcl 8813  ax-addrcl 8814  ax-mulcl 8815  ax-mulrcl 8816  ax-mulcom 8817  ax-addass 8818  ax-mulass 8819  ax-distr 8820  ax-i2m1 8821  ax-1ne0 8822  ax-1rid 8823  ax-rnegex 8824  ax-rrecex 8825  ax-cnre 8826  ax-pre-lttri 8827  ax-pre-lttrn 8828  ax-pre-ltadd 8829  ax-pre-mulgt0 8830
This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-3or 935  df-3an 936  df-tru 1310  df-ex 1532  df-nf 1535  df-sb 1639  df-eu 2160  df-mo 2161  df-clab 2283  df-cleq 2289  df-clel 2292  df-nfc 2421  df-ne 2461  df-nel 2462  df-ral 2561  df-rex 2562  df-reu 2563  df-rmo 2564  df-rab 2565  df-v 2803  df-sbc 3005  df-csb 3095  df-dif 3168  df-un 3170  df-in 3172  df-ss 3179  df-pss 3181  df-nul 3469  df-if 3579  df-pw 3640  df-sn 3659  df-pr 3660  df-tp 3661  df-op 3662  df-uni 3844  df-iun 3923  df-br 4040  df-opab 4094  df-mpt 4095  df-tr 4130  df-eprel 4321  df-id 4325  df-po 4330  df-so 4331  df-fr 4368  df-we 4370  df-ord 4411  df-on 4412  df-lim 4413  df-suc 4414  df-om 4673  df-xp 4711  df-rel 4712  df-cnv 4713  df-co 4714  df-dm 4715  df-rn 4716  df-res 4717  df-ima 4718  df-iota 5235  df-fun 5273  df-fn 5274  df-f 5275  df-f1 5276  df-fo 5277  df-f1o 5278  df-fv 5279  df-ov 5877  df-oprab 5878  df-mpt2 5879  df-2nd 6139  df-riota 6320  df-recs 6404  df-rdg 6439  df-er 6676  df-en 6880  df-dom 6881  df-sdom 6882  df-pnf 8885  df-mnf 8886  df-xr 8887  df-ltxr 8888  df-le 8889  df-sub 9055  df-neg 9056  df-div 9440  df-nn 9763  df-2 9820  df-3 9821  df-4 9822  df-n0 9982  df-z 10041  df-uz 10247  df-rp 10371  df-seq 11063  df-exp 11121  df-fac 11305
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