Lang Son: BiiVdn Ngoc, l2A, THPT Chu Van An;
Phf Tho: N guydn Quang Huy,l2T, THPT chuy€n Hirng Vuong; Bdc Giang: L€ Trung Ki€n, I lT, THm chuydn
Bic Giang; Bdc Ninh: Nguyen Tri Dung, llAt. THPf ThuAn Th)nh; Vinh Phric: VrtVdn Quang, 1241, THPf
chuy6n Vlnh Phric; Hi Ndi: Hd Minh Tud'n, llA2,
THPT chuy€n DHKHTN. Ngutdn Quang Kidn, llAl,
THPT chuydn DHSP; Hi Tnyt Li Dltc Trong, llT,
THPT chuydn Nguy0n Hu0, Hi DOng; Nam Dinh: NguydnVdn Dinh,12I, THFrf Giao Thuy; Hii Duong: Vfi Xudn Drong, 1lT, THP| chuydn Nguydn Trdi; Htrng Ydnz Phan Ti€h Dfing, l1T, THPT chuydn Hung YCn; Hda Binh: V{i Vi€r Diing, llT, THm chuydn Ho}rng
Van Thu; Th6i Binh: NguydnThi HaTrang,llT, THm
chuy€n Thrii Binh; Thanh H6az Trinh Hii Linh, llT,
THPT chuy6n Lam Son; Ngh€ An: Tb H6ng San, 1 1A1, THPT Phan Boi Chau; Hi finh: Trdn Dinh Crdng,llT,
THPT chuydn Hd TTnh; Thla Thi€n - Hue: Nguyin
Tuiih Minh, l2T, THFrf chuy€n Qu6c hoc Hue; Di
NIng: P/ran Thi QuynhTrdn, llAl, THFrf chuyOn Ld
Quf DOn; Khdnh Hba: Nga.yir Thi Hodng Oanh, llT,
THPT chuyon Le Quf Don, Nha Trang; Quing Ngii:
Trdn Ngoc Hi€u, 11T, THFT chuyen Le Khidt; Quing
Triz Vd Xhn Thiy, l0T, THfrf chuyOn Le Quf DOn; Quing Binb: Ddng Ngoc Thanh, l1T, THm chuyOn
Quring Binh; Gia Lai: TrdnThanh Nam, 12C3,THW
Hing Vuong; Dak Lnk: L€ Dirc Quang, 1lCT, THPf
chuy6n Nguydn Du; Bi Ria - Vflng Tiu: Nguy|n L€
Vdn, l2Al3, THPT V[ng Tiu, TP Vfrng T]u; TP H6
Chi Minh: Nguy?n Hoting Dting, llT, THru Nguyen Thuong Hidn; Crin ThotVd Qudc Bd Crrir, 10A1, THPT chuyOn Ly Tu Trong, TP CdnTho; Phri Y6n: Trdn Hd
Tlmnh Phti, I lT, THm chuyon Luong Van Chrinh; Bin
Trez L€ Vdn Chdnh, 1lT, THm B€-n Tre; Ci Mau:
Clfiu Ngoc Huy,l2Al, THPT Ddm Doi.-
NGUYEN VAN MAU
Bni T1t/339. Trong mar phiing cho dtdng
trin tant O bdn klnh r. Ldj,diO'rn P co'dinh nant
b4n trottg dtrdng trdn t'ii OP = d > 0. Hai day
cung AB t,d Ci ai clua clid"nt P tao tlfitth nfir
gdc a klfiug ddi (0" < a <90").Tinh giri rri ldn nhtii vd gid rri nhri nlru't ct)a tdng AB + CD klti hai ddy AB, CD thay doi y'd rdr: dinh vi trl ctiu cdc day AB, CD d6.
Ldi giii. Tim gi6 tri nh6 nhat cria AB+CD lit
bli to6n kh6, chua c6 ldi giii. Sau ddy ld cdch
tim gid rri ldn nhdi cila AB+CD.
Goi 11, K ldn luot li hinh chidu c[ra O trln AB, CD. Goi 1 li trung didm cira OP vd M lb hinh
chidu cira I fiCn HK (xem hinh vd).
2