Tính giới hạn của dãy số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabg2da9maaqahabaWaaSaaaeaacaaIYaGa % am4AaiabgkHiTiaaigdaaeaacaaIYaWaaWbaaSqabeaacaWGRbaaaa % aaaeaacaWGRbGaeyypa0JaaGymaaqaaiaad6gaa0GaeyyeIuoaaaa!4435! {u_n} = \sum\limits_{k = 1}^n {\frac{{2k - 1}}{{{2^k}}}} \)
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Lời giải:
Báo saiTa có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabgkHiTmaalaaabaGaaGymaaqaaiaaikda % aaGaamyDamaaBaaaleaacaWGUbaabeaakiabg2da9maalaaabaGaaG % ymaaqaaiaaikdaaaGaey4kaSYaaeWaaeaadaWcaaqaaiaaigdaaeaa % caaIYaaaaiabgUcaRmaalaaabaGaaGymaaqaaiaaikdadaahaaWcbe % qaaiaaikdaaaaaaOGaey4kaSIaaiOlaiaac6cacaGGUaGaey4kaSYa % aSaaaeaacaaIXaaabaGaaGOmamaaCaaaleqabaGaamOBaiabgkHiTi % aaigdaaaaaaaGccaGLOaGaayzkaaGaeyOeI0YaaSaaaeaacaaIYaGa % amOBaiabgkHiTiaaigdaaeaacaaIYaWaaWbaaSqabeaacaWGUbGaey % 4kaSIaaGymaaaaaaaaaa!5689! {u_n} - \frac{1}{2}{u_n} = \frac{1}{2} + \left( {\frac{1}{2} + \frac{1}{{{2^2}}} + ... + \frac{1}{{{2^{n - 1}}}}} \right) - \frac{{2n - 1}}{{{2^{n + 1}}}}\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H49aaS % aaaeaacaaIXaaabaGaaGOmaaaacaWG1bWaaSbaaSqaaiaad6gaaeqa % aOGaeyypa0ZaaSaaaeaacaaIZaaabaGaaGOmaaaacqGHsisldaWcaa % qaaiaaikdacaWGUbGaey4kaSIaaGymaaqaaiaaikdadaahaaWcbeqa % aiaad6gacqGHRaWkcaaIXaaaaaaakiabgkDiElGacYgacaGGPbGaai % yBaiaadwhadaWgaaWcbaGaamOBaaqabaGccqGH9aqpcaaIZaaaaa!4F69! \Rightarrow \frac{1}{2}{u_n} = \frac{3}{2} - \frac{{2n + 1}}{{{2^{n + 1}}}} \Rightarrow \lim {u_n} = 3\)