Gravesande, Willem Jacob 's, Physices elementa mathematica, experimentis confirmata sive introductio ad philosophiam Newtonianam; Tom. 1
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247160PHYSICES ELEMENTA
SCHOLIUM I.
Uberior demonſtratio n. 558.
Demonſtravimus in congreſſu corporum elaſticorum ſummam virium ante
11TAB. XX.
fig. 12.
&
poſt ictum eſſe eandem ; unde ſequitur, poſitis explicatis in n. 565. 566. AB x BNq + BC x BEq = AB x BGq + BC x BPq; cujus & hìc geometri-
22470. cam dabimus demonſtrationem.
Primo tendant corpora eandem partem verſus. Formentur quadrata li-
33587. nearum BE, BG, BN, &
BP; ducatur omnium diagonalis BV. Du-
44TAB. XX.
fig. 18.
catur IS parallela ad PV;
& per S, punctum, in quo diagonalem ſecat,
ducatur XSK, parallela PB;
continuentur GR & EQ in Z & K; quia
IN &
IG ſunt æquales, ut & IP & IE, triangula YST, RSZ ſunt æ-
qualia, etiam triangula SXV, SKQ.
Idcirca Trapezium GRTN æ-
quale eſt rectangulo GZYN, &
trapezium EQVP æquale rectangulo
EKXP.
Semidifferentia quadratorum linearum BN, BG eſt trapezium GRTN,
id eſt rectangulum GZYN.
Eodem modo ſemidifterentia quadratorum linea-
rum BP, BE eſt rectangulum EKXP;
Sed rectangula hæc, propter communem
altitudinem IS, ſunt ut baſes , aut ut baſium ſemiſſes IN, IE;
etiam 551. El. VI. ſunt ſemidifferentiæ quadratorum ita integræ differentiæ: ergo
BNq - BGq, BPq - BEq: :IN, IE, id eſt ut BC ad AB ex conſtructione.
Idcirco AB x BNq - AB x BGq = BC x BPq - BC x BEq; ideo AB x BNq
+ BC x BEq = AB x BGq + BC x BPq.
quod demonſtrandum erat.
Tendant nunc corpora in partes contrarias. Formentur iterum quadrata
66588. linearum BP, BN, BE aut B e, &
BG aut B g. Propter æquales IN,
77TAB. XX.
fig. 29.
IG, &
IP, IE, æquales ſunt NP, EG, aut e g; addamus utrim-
que e N, erunt æquales e P, g N.
Differentia quadratorum BV & BQ,
id eſt quadratorum linearum BP, BE, eſt rectangulum, cujus baſis eſt PV,
&
e Q, id eſt PE, & altitudo e P; differentia quadratorum BT, BR,
id eſt quadratorum linearum BN, B g aut BG, eſt rectangulum, cujus ba-
ſis eſt NT, &
g R, id eſt NG, & altitudo g N; propter æquales alti-
tudines rectangula hæc ſunt ut baſes PE, NG, aut ut harum ſemiſſes IE,
IN, quæ ſuntut AB, BC;
ergo
BPq - BEq, BNq - BGq:
: AB, BC
Idcirco AB x BNq - AB x BGq = BC x BPq - BC x BEq; unde
deducimus AB x BNq + BC x BEq = AB x BGq + BC x BPq.
Quod
demonſtrandum erat.

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