Phucrng ph6p v6t kiQt ld mQt c6ng.cg t6t dtl chrmg
minfr mQi c6ng thirc khi da UiCt t6t qui, nhrmg 14i
kh6 kh6m ph61a cdc ktSt qu6. o6 ttric ph+c diAu d6, Archimedes dddua taphwongphdp cdn Ddzrg' N6 duo.c
tim th6y trong mQt bin sao luQn v[n cit, Archimedes ghi Eratosthenes (ldtoitng 230 ndm TCN).
"
Tu tudng chinh cira P\uong ph6p.ndy ld: d6 tim mQt
diQn tich hoflc mQt th6 tich it i .it n6 thinh mot s6
r6t 16n chc giiti phdng m6ng song song ho[c c5c lop m6ng song song vit tu&ng tucrng treo chirng 6 m6t
diu tdm di dugc x5c tlinh.
Blri toin 3. Tinh th€ tich hinh ciu bi€t bdn k{nh cua n6 bdng r.
DAt hinh cdu d6 cho cr)ng dutrng kffi cr,rc cira n6 dgc theo mQt clrc nim ngang r'r vdi cqc bdc Ntpi
g6c (h.3). Dr.mg mQt hinh tru vd mQt hinh n6n trdn xoay bing c6ch cho quay hinh ohtt.rhAr NABS qr-!
truc x x. Bay gid .6t to Uu hinh kh6i t16 nhirng 16t cnt
tfrang Aung (thua nhan ring chring d6u ld nhimg hinhlru de.t) c6ch t/ mQt khoa"g bing x vd c6 chiiru
ddy ld Ar. Theo ktit qub Bdi todn2,th6 tich cuacdcllt
cic l6t cit niry ta duoc 2r (V + Vz) = 4r.4'
Tn dtt 2r(, \ r). +) = snra . Suy ra I/ = +
Diy ld l<ri giii oia Archimedes fiong method' Tuy
nnien Uan thdn 6ng kh6ng ydn tdmvoi loi giAi d6 vd ild sri dpng phucrng ph6p vet kiQt de dua ra mQt ph6p
chimg minh chdt chE.
Tron! phuong ph6p c6n bing, ta nhin thlV su dgp dE ctra /tuong
"1 *qt d9 16n the tich c6 thr5 xem ld hqp boi m6t sO dtr ton c6c bQ phQn nguyCn tu' R6 rdng so
v6i phucrng ph5p hiQn dpi v6 gi6i han thi phuong
ph6p cAn iaig ciu A'r"himedes c6 th6 ldm cho n6 trd
inarl,
"fr[t chE vd vC co bin gi6ng nhu
ph6p tinh tich
phdn hiQn nay.