Tính giới hạn của dãy số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabg2da9iaacIcacaaIXaGaeyOeI0YaaSaa % aeaacaaIXaaabaGaamivamaaBaaaleaacaaIXaaabeaaaaGccaGGPa % GaaiikaiaaigdacqGHsisldaWcaaqaaiaaigdaaeaacaWGubWaaSba % aSqaaiaaikdaaeqaaaaakiaacMcacaGGUaGaaiOlaiaac6cacaGGOa % GaaGymaiabgkHiTmaalaaabaGaaGymaaqaaiaadsfadaWgaaWcbaGa % amOBaaqabaaaaOGaaiykaaaa!4C2E! {u_n} = (1 - \frac{1}{{{T_1}}})(1 - \frac{1}{{{T_2}}})...(1 - \frac{1}{{{T_n}}})\) trong đó \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivamaaBa % aaleaacaWGUbaabeaakiabg2da9maalaaabaGaamOBaiaacIcacaWG % UbGaey4kaSIaaGymaiaacMcaaeaacaaIYaaaaaaa!3EA4! {T_n} = \frac{{n(n + 1)}}{2}\).
Suy nghĩ và trả lời câu hỏi trước khi xem đáp án
Lời giải:
Báo saiTa có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiabgk % HiTmaalaaabaGaaGymaaqaaiaadsfadaWgaaWcbaGaam4Aaaqabaaa % aOGaeyypa0JaaGymaiabgkHiTmaalaaabaGaaGOmaaqaaiaadUgaca % GGOaGaam4AaiabgUcaRiaaigdacaGGPaaaaiabg2da9maalaaabaGa % aiikaiaadUgacqGHsislcaaIXaGaaiykaiaacIcacaWGRbGaey4kaS % IaaGOmaiaacMcaaeaacaWGRbGaaiikaiaadUgacqGHRaWkcaaIXaGa % aiykaaaaaaa!507A! 1 - \frac{1}{{{T_k}}} = 1 - \frac{2}{{k(k + 1)}} = \frac{{(k - 1)(k + 2)}}{{k(k + 1)}}\)
Suy ra \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabg2da9maalaaabaGaaGymaaqaaiaaioda % aaGaaiOlamaalaaabaGaamOBaiabgUcaRiaaikdaaeaacaWGUbaaai % abgkDiElGacYgacaGGPbGaaiyBaiaadwhadaWgaaWcbaGaamOBaaqa % baGccqGH9aqpdaWcaaqaaiaaigdaaeaacaaIZaaaaaaa!48C9! {u_n} = \frac{1}{3}.\frac{{n + 2}}{n} \Rightarrow \lim {u_n} = \frac{1}{3}\)