chordthmlem5 - Metamath Proof Explorer

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Theorem chordthmlem5 26092

Description: If P is on the segment AB and AQ = BQ, then PA · PB = BQ ² − PQ ² . This follows from two uses of chordthmlem3 26090 to show that PQ ² = QM ² + PM ² and BQ ² = QM ² + BM ² , so BQ ² − PQ ² = (QM ² + BM ² ) − (QM ² + PM ² ) = BM ² − PM ² , which equals PA · PB by chordthmlem4 26091. (Contributed by David Moews, 28-Feb-2017.)

**Hypotheses**
Ref	Expression
chordthmlem5.A	⊢ (𝜑 → 𝐴 ∈ ℂ)
chordthmlem5.B	⊢ (𝜑 → 𝐵 ∈ ℂ)
chordthmlem5.Q	⊢ (𝜑 → 𝑄 ∈ ℂ)
chordthmlem5.X	⊢ (𝜑 → 𝑋 ∈ (0[,]1))
chordthmlem5.P	⊢ (𝜑 → 𝑃 = ((𝑋 · 𝐴) + ((1 − 𝑋) · 𝐵)))
chordthmlem5.ABequidistQ	⊢ (𝜑 → (abs‘(𝐴 − 𝑄)) = (abs‘(𝐵 − 𝑄)))

**Assertion**
Ref	Expression
chordthmlem5	⊢ (𝜑 → ((abs‘(𝑃 − 𝐴)) · (abs‘(𝑃 − 𝐵))) = (((abs‘(𝐵 − 𝑄))↑2) − ((abs‘(𝑃 − 𝑄))↑2)))

**Proof of Theorem chordthmlem5**
Step	Hyp	Ref	Expression
1		chordthmlem5.Q	. . . . . . 7 ⊢ (𝜑 → 𝑄 ∈ ℂ)
2		chordthmlem5.A	. . . . . . . . 9 ⊢ (𝜑 → 𝐴 ∈ ℂ)
3		chordthmlem5.B	. . . . . . . . 9 ⊢ (𝜑 → 𝐵 ∈ ℂ)
4	2, 3	addcld 11095	. . . . . . . 8 ⊢ (𝜑 → (𝐴 + 𝐵) ∈ ℂ)
5	4	halfcld 12319	. . . . . . 7 ⊢ (𝜑 → ((𝐴 + 𝐵) / 2) ∈ ℂ)
6	1, 5	subcld 11433	. . . . . 6 ⊢ (𝜑 → (𝑄 − ((𝐴 + 𝐵) / 2)) ∈ ℂ)
7	6	abscld 15247	. . . . 5 ⊢ (𝜑 → (abs‘(𝑄 − ((𝐴 + 𝐵) / 2))) ∈ ℝ)
8	7	recnd 11104	. . . 4 ⊢ (𝜑 → (abs‘(𝑄 − ((𝐴 + 𝐵) / 2))) ∈ ℂ)
9	8	sqcld 13963	. . 3 ⊢ (𝜑 → ((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) ∈ ℂ)
10	3, 5	subcld 11433	. . . . . 6 ⊢ (𝜑 → (𝐵 − ((𝐴 + 𝐵) / 2)) ∈ ℂ)
11	10	abscld 15247	. . . . 5 ⊢ (𝜑 → (abs‘(𝐵 − ((𝐴 + 𝐵) / 2))) ∈ ℝ)
12	11	recnd 11104	. . . 4 ⊢ (𝜑 → (abs‘(𝐵 − ((𝐴 + 𝐵) / 2))) ∈ ℂ)
13	12	sqcld 13963	. . 3 ⊢ (𝜑 → ((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2) ∈ ℂ)
14		chordthmlem5.P	. . . . . . . 8 ⊢ (𝜑 → 𝑃 = ((𝑋 · 𝐴) + ((1 − 𝑋) · 𝐵)))
15		unitssre 13332	. . . . . . . . . . . 12 ⊢ (0[,]1) ⊆ ℝ
16		chordthmlem5.X	. . . . . . . . . . . 12 ⊢ (𝜑 → 𝑋 ∈ (0[,]1))
17	15, 16	sselid 3930	. . . . . . . . . . 11 ⊢ (𝜑 → 𝑋 ∈ ℝ)
18	17	recnd 11104	. . . . . . . . . 10 ⊢ (𝜑 → 𝑋 ∈ ℂ)
19	18, 2	mulcld 11096	. . . . . . . . 9 ⊢ (𝜑 → (𝑋 · 𝐴) ∈ ℂ)
20		1cnd 11071	. . . . . . . . . . 11 ⊢ (𝜑 → 1 ∈ ℂ)
21	20, 18	subcld 11433	. . . . . . . . . 10 ⊢ (𝜑 → (1 − 𝑋) ∈ ℂ)
22	21, 3	mulcld 11096	. . . . . . . . 9 ⊢ (𝜑 → ((1 − 𝑋) · 𝐵) ∈ ℂ)
23	19, 22	addcld 11095	. . . . . . . 8 ⊢ (𝜑 → ((𝑋 · 𝐴) + ((1 − 𝑋) · 𝐵)) ∈ ℂ)
24	14, 23	eqeltrd 2837	. . . . . . 7 ⊢ (𝜑 → 𝑃 ∈ ℂ)
25	24, 5	subcld 11433	. . . . . 6 ⊢ (𝜑 → (𝑃 − ((𝐴 + 𝐵) / 2)) ∈ ℂ)
26	25	abscld 15247	. . . . 5 ⊢ (𝜑 → (abs‘(𝑃 − ((𝐴 + 𝐵) / 2))) ∈ ℝ)
27	26	recnd 11104	. . . 4 ⊢ (𝜑 → (abs‘(𝑃 − ((𝐴 + 𝐵) / 2))) ∈ ℂ)
28	27	sqcld 13963	. . 3 ⊢ (𝜑 → ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2) ∈ ℂ)
29	9, 13, 28	pnpcand 11470	. 2 ⊢ (𝜑 → ((((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2)) − (((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2))) = (((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2) − ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2)))
30		0red 11079	. . . 4 ⊢ (𝜑 → 0 ∈ ℝ)
31		eqidd 2737	. . . 4 ⊢ (𝜑 → ((𝐴 + 𝐵) / 2) = ((𝐴 + 𝐵) / 2))
32	2	mul02d 11274	. . . . . 6 ⊢ (𝜑 → (0 · 𝐴) = 0)
33	20	subid1d 11422	. . . . . . . 8 ⊢ (𝜑 → (1 − 0) = 1)
34	33	oveq1d 7352	. . . . . . 7 ⊢ (𝜑 → ((1 − 0) · 𝐵) = (1 · 𝐵))
35	3	mulid2d 11094	. . . . . . 7 ⊢ (𝜑 → (1 · 𝐵) = 𝐵)
36	34, 35	eqtrd 2776	. . . . . 6 ⊢ (𝜑 → ((1 − 0) · 𝐵) = 𝐵)
37	32, 36	oveq12d 7355	. . . . 5 ⊢ (𝜑 → ((0 · 𝐴) + ((1 − 0) · 𝐵)) = (0 + 𝐵))
38	3	addid2d 11277	. . . . 5 ⊢ (𝜑 → (0 + 𝐵) = 𝐵)
39	37, 38	eqtr2d 2777	. . . 4 ⊢ (𝜑 → 𝐵 = ((0 · 𝐴) + ((1 − 0) · 𝐵)))
40		chordthmlem5.ABequidistQ	. . . 4 ⊢ (𝜑 → (abs‘(𝐴 − 𝑄)) = (abs‘(𝐵 − 𝑄)))
41	2, 3, 1, 30, 31, 39, 40	chordthmlem3 26090	. . 3 ⊢ (𝜑 → ((abs‘(𝐵 − 𝑄))↑2) = (((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2)))
42	2, 3, 1, 17, 31, 14, 40	chordthmlem3 26090	. . 3 ⊢ (𝜑 → ((abs‘(𝑃 − 𝑄))↑2) = (((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2)))
43	41, 42	oveq12d 7355	. 2 ⊢ (𝜑 → (((abs‘(𝐵 − 𝑄))↑2) − ((abs‘(𝑃 − 𝑄))↑2)) = ((((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2)) − (((abs‘(𝑄 − ((𝐴 + 𝐵) / 2)))↑2) + ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2))))
44	2, 3, 16, 31, 14	chordthmlem4 26091	. 2 ⊢ (𝜑 → ((abs‘(𝑃 − 𝐴)) · (abs‘(𝑃 − 𝐵))) = (((abs‘(𝐵 − ((𝐴 + 𝐵) / 2)))↑2) − ((abs‘(𝑃 − ((𝐴 + 𝐵) / 2)))↑2)))
45	29, 43, 44	3eqtr4rd 2787	1 ⊢ (𝜑 → ((abs‘(𝑃 − 𝐴)) · (abs‘(𝑃 − 𝐵))) = (((abs‘(𝐵 − 𝑄))↑2) − ((abs‘(𝑃 − 𝑄))↑2)))

Colors of variables: wff setvar class

Syntax hints: → wi 4 = wceq 1540 ∈ wcel 2105 ‘cfv 6479 (class class class)co 7337 ℂcc 10970 ℝcr 10971 0cc0 10972 1c1 10973 + caddc 10975 · cmul 10977 − cmin 11306 / cdiv 11733 2c2 12129 [,]cicc 13183 ↑cexp 13883 abscabs 15044

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1912 ax-6 1970 ax-7 2010 ax-8 2107 ax-9 2115 ax-10 2136 ax-11 2153 ax-12 2170 ax-ext 2707 ax-rep 5229 ax-sep 5243 ax-nul 5250 ax-pow 5308 ax-pr 5372 ax-un 7650 ax-inf2 9498 ax-cnex 11028 ax-resscn 11029 ax-1cn 11030 ax-icn 11031 ax-addcl 11032 ax-addrcl 11033 ax-mulcl 11034 ax-mulrcl 11035 ax-mulcom 11036 ax-addass 11037 ax-mulass 11038 ax-distr 11039 ax-i2m1 11040 ax-1ne0 11041 ax-1rid 11042 ax-rnegex 11043 ax-rrecex 11044 ax-cnre 11045 ax-pre-lttri 11046 ax-pre-lttrn 11047 ax-pre-ltadd 11048 ax-pre-mulgt0 11049 ax-pre-sup 11050 ax-addf 11051 ax-mulf 11052

This theorem depends on definitions: df-bi 206 df-an 397 df-or 845 df-3or 1087 df-3an 1088 df-tru 1543 df-fal 1553 df-ex 1781 df-nf 1785 df-sb 2067 df-mo 2538 df-eu 2567 df-clab 2714 df-cleq 2728 df-clel 2814 df-nfc 2886 df-ne 2941 df-nel 3047 df-ral 3062 df-rex 3071 df-rmo 3349 df-reu 3350 df-rab 3404 df-v 3443 df-sbc 3728 df-csb 3844 df-dif 3901 df-un 3903 df-in 3905 df-ss 3915 df-pss 3917 df-nul 4270 df-if 4474 df-pw 4549 df-sn 4574 df-pr 4576 df-tp 4578 df-op 4580 df-uni 4853 df-int 4895 df-iun 4943 df-iin 4944 df-br 5093 df-opab 5155 df-mpt 5176 df-tr 5210 df-id 5518 df-eprel 5524 df-po 5532 df-so 5533 df-fr 5575 df-se 5576 df-we 5577 df-xp 5626 df-rel 5627 df-cnv 5628 df-co 5629 df-dm 5630 df-rn 5631 df-res 5632 df-ima 5633 df-pred 6238 df-ord 6305 df-on 6306 df-lim 6307 df-suc 6308 df-iota 6431 df-fun 6481 df-fn 6482 df-f 6483 df-f1 6484 df-fo 6485 df-f1o 6486 df-fv 6487 df-isom 6488 df-riota 7293 df-ov 7340 df-oprab 7341 df-mpo 7342 df-of 7595 df-om 7781 df-1st 7899 df-2nd 7900 df-supp 8048 df-frecs 8167 df-wrecs 8198 df-recs 8272 df-rdg 8311 df-1o 8367 df-2o 8368 df-er 8569 df-map 8688 df-pm 8689 df-ixp 8757 df-en 8805 df-dom 8806 df-sdom 8807 df-fin 8808 df-fsupp 9227 df-fi 9268 df-sup 9299 df-inf 9300 df-oi 9367 df-card 9796 df-pnf 11112 df-mnf 11113 df-xr 11114 df-ltxr 11115 df-le 11116 df-sub 11308 df-neg 11309 df-div 11734 df-nn 12075 df-2 12137 df-3 12138 df-4 12139 df-5 12140 df-6 12141 df-7 12142 df-8 12143 df-9 12144 df-n0 12335 df-z 12421 df-dec 12539 df-uz 12684 df-q 12790 df-rp 12832 df-xneg 12949 df-xadd 12950 df-xmul 12951 df-ioo 13184 df-ioc 13185 df-ico 13186 df-icc 13187 df-fz 13341 df-fzo 13484 df-fl 13613 df-mod 13691 df-seq 13823 df-exp 13884 df-fac 14089 df-bc 14118 df-hash 14146 df-shft 14877 df-cj 14909 df-re 14910 df-im 14911 df-sqrt 15045 df-abs 15046 df-limsup 15279 df-clim 15296 df-rlim 15297 df-sum 15497 df-ef 15876 df-sin 15878 df-cos 15879 df-pi 15881 df-struct 16945 df-sets 16962 df-slot 16980 df-ndx 16992 df-base 17010 df-ress 17039 df-plusg 17072 df-mulr 17073 df-starv 17074 df-sca 17075 df-vsca 17076 df-ip 17077 df-tset 17078 df-ple 17079 df-ds 17081 df-unif 17082 df-hom 17083 df-cco 17084 df-rest 17230 df-topn 17231 df-0g 17249 df-gsum 17250 df-topgen 17251 df-pt 17252 df-prds 17255 df-xrs 17310 df-qtop 17315 df-imas 17316 df-xps 17318 df-mre 17392 df-mrc 17393 df-acs 17395 df-mgm 18423 df-sgrp 18472 df-mnd 18483 df-submnd 18528 df-mulg 18797 df-cntz 19019 df-cmn 19483 df-psmet 20695 df-xmet 20696 df-met 20697 df-bl 20698 df-mopn 20699 df-fbas 20700 df-fg 20701 df-cnfld 20704 df-top 22149 df-topon 22166 df-topsp 22188 df-bases 22202 df-cld 22276 df-ntr 22277 df-cls 22278 df-nei 22355 df-lp 22393 df-perf 22394 df-cn 22484 df-cnp 22485 df-haus 22572 df-tx 22819 df-hmeo 23012 df-fil 23103 df-fm 23195 df-flim 23196 df-flf 23197 df-xms 23579 df-ms 23580 df-tms 23581 df-cncf 24147 df-limc 25136 df-dv 25137 df-log 25818

This theorem is referenced by: chordthm 26093 chordthmALT 42883

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