Cho cấp số nhân \((u_n)\) có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaaIXaaabeaakiabg2da9iaaigdacaGGSaGaamyDamaaBaaa % leaacaaIYaaabeaakiabg2da9iabgkHiTiaaikdaaaa!3EEB! {u_1} = 1,{u_2} = - 2\) . Mệnh đề nào sau đây đúng?
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Lời giải:
Báo saiGọi q là công bội của CSN đã cho, ta có: \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyDamaaBa % aaleaacaaIXaaabeaakiabg2da9iaaigdacaGG7aGaamyDamaaBaaa % leaacaaIYaaabeaakiabg2da9iabgkHiTiaaikdacqGHshI3caWGXb % Gaeyypa0ZaaSaaaeaacaWG1bWaaSbaaSqaaiaaikdaaeqaaaGcbaGa % amyDamaaBaaaleaacaaIXaaabeaaaaGccqGH9aqpdaWcaaqaaiabgk % HiTiaaikdaaeaacaaIXaaaaiabg2da9iabgkHiTiaaikdaaaa!4D63! {u_1} = 1;{u_2} = - 2 \Rightarrow q = \frac{{{u_2}}}{{{u_1}}} = \frac{{ - 2}}{1} = - 2\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H4Taam % yDamaaBaaaleaacaaIYaGaaGimaiaaigdacaaI5aaabeaakiabg2da % 9iaadwhadaWgaaWcbaGaaGymaaqabaGccaGGUaGaamyCamaaCaaale % qabaGaaGOmaiaaicdacaaIXaGaaGioaaaakiabg2da9iaaigdacaGG % UaWaaeWaaeaacqGHsislcaaIYaaacaGLOaGaayzkaaWaaWbaaSqabe % aacaaIYaGaaGimaiaaigdacaaI4aaaaOGaeyypa0JaaGOmamaaCaaa % leqabaGaaGOmaiaaicdacaaIXaGaaGioaaaaaaa!51E9! \Rightarrow {u_{2019}} = {u_1}.{q^{2018}} = 1.{\left( { - 2} \right)^{2018}} = {2^{2018}}\)
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 4