Tìm lim \(u_n\) biết \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabg2da9maayaaabaWaaOaaaeaacaaIYaWa % aOaaaeaacaaIYaGaaiOlaiaac6cacaGGUaWaaOaaaeaacaaIYaaale % qaaaqabaaabeaaaeaacaWGUbGaaeiiaiaabsgacaqGHbGaaeyDaiaa % bccacaqGJbGaaeyyaiaab6gaaOGaayjo+daaaa!474E! {u_n} = \underbrace {\sqrt {2\sqrt {2...\sqrt 2 } } }_{n{\rm{ dau can}}}\)
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaWGUbaabeaakiabg2da9iaaikdadaahaaWcbeqaamaalaaa % baGaaGymaaqaaiaaikdaaaGaey4kaSYaaSaaaeaacaaIXaaabaGaaG % OmamaaCaaameqabaGaaGOmaaaaaaWccqGHRaWkcaGGUaGaaiOlaiaa % c6cacqGHRaWkdaWcaaqaaiaaigdaaeaacaaIYaWaaWbaaWqabeaaca % WGUbaaaaaaaaGccqGH9aqpcaaIYaWaaWbaaSqabeaacaaIXaGaeyOe % I0YaaeWaaeaadaWcaaqaaiaaigdaaeaacaaIYaaaaaGaayjkaiaawM % caamaaCaaameqabaGaamOBaaaaaaaaaa!4D3F! {u_n} = {2^{\frac{1}{2} + \frac{1}{{{2^2}}} + ... + \frac{1}{{{2^n}}}}} = {2^{1 - {{\left( {\frac{1}{2}} \right)}^n}}}\) nên \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaacM % gacaGGTbGaamyDamaaBaaaleaacaWGUbaabeaakiabg2da9iGacYga % caGGPbGaaiyBaiaaikdadaahaaWcbeqaaiaaigdacqGHsisldaqada % qaamaalaaabaGaaGymaaqaaiaaikdaaaaacaGLOaGaayzkaaWaaWba % aWqabeaacaWGUbaaaaaakiabg2da9iaaikdaaaa!474B! \lim {u_n} = \lim {2^{1 - {{\left( {\frac{1}{2}} \right)}^n}}} = 2\)