Tìm tất cả giá trị thực của tham số m để bất phương trình \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaaiaaiodaaeqaaOWaaeWaaeaacaWG4bWaaWba % aSqabeaacaaIYaaaaOGaey4kaSIaaGinaiaadIhacqGHRaWkcaWGTb % aacaGLOaGaayzkaaGaeyyzImRaaGymaaaa!4421! {\log _3}\left( {{x^2} + 4x + m} \right) \ge 1\) nghiệm đúng với mọi ?
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaaiaaiodaaeqaaOWaaeWaaeaacaWG4bWaaWba % aSqabeaacaaIYaaaaOGaey4kaSIaaGinaiaadIhacqGHRaWkcaWGTb % aacaGLOaGaayzkaaGaeyyzImRaaGymaiaabccacqGHaiIicaWG4bGa % eyicI4SaeSyhHeQaeyi1HSTaamiEamaaCaaaleqabaGaaGOmaaaaki % abgUcaRiaaisdacaWG4bGaey4kaSIaamyBaiabgkHiTiaaiodacqGH % LjYScaaIWaGaaeiiaiabgcGiIiaadIhacqGHiiIZcqWIDesOcqGHuh % Y2cqqHuoarcqGHKjYOcaaIWaGaeyi1HSTaamyBaiabgwMiZkaaiEda % aaa!67D6! {\log _3}\left( {{x^2} + 4x + m} \right) \ge 1{\rm{ }}\forall x \in R \Leftrightarrow {x^2} + 4x + m - 3 \ge 0{\rm{ }}\forall x \in R \Leftrightarrow \Delta \le 0 \Leftrightarrow m \ge 7\)