... Tac6:L = 10 1g— v6i li thi Lj = lOIg^ (1) vail 2thi L2 =10 1g^ (2) Tu(l)va (2) L2 -L, =10 1g^ -10 1giL = ioigIl Vi: U -L] =20 = ^20 = 10 1g^^^ = 10 2 =10 0. Chpn dap an C &apos ;1 M cau ... l=k—+—= 2 4 k + - 2, k+- 2 Dat: fk = k + - 2 V 2I k + - 2 (1) V 21 94=; f 1 ^ V f 1^ 2 V k + + l kH I 2 J 2T" ' 2y 21 "^ 21 fk+l -Tu (1) va (2) ta ... f, va (2 la hai tan so lien tiep fj < £3 thi kj va kj la 2 so nguyen lien tiep: k2 = k| +1 Nhu vay ta co: — = — 1 _ f2 40 60 ki k2 kj ki +1 k, ki +1 , , k 21 21 fi 2 .1, 2. 40 ,...