Tìm tất cả giá trị thực của tham số m để bất phương trình \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaamaalaaabaGaaGymaaqaaiaaiwdaaaaabeaa % kmaabmaabaGaamyBaiaadIhacqGHsislcaWG4bWaaWbaaSqabeaaca % aIYaaaaaGccaGLOaGaayzkaaGaeyizImQaciiBaiaac+gacaGGNbWa % aSbaaSqaamaalaaabaGaaGymaaqaaiaaiwdaaaaabeaakiaaisdaaa % a!47DB! {\log _{\frac{1}{5}}}\left( {mx - {x^2}} \right) \le {\log _{\frac{1}{5}}}4\) vô nghiệm?
Hãy suy nghĩ và trả lời câu hỏi trước khi xem đáp án
Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaamaalaaabaGaaGymaaqaaiaaiwdaaaaabeaa % kmaabmaabaGaamyBaiaadIhacqGHsislcaWG4bWaaWbaaSqabeaaca % aIYaaaaaGccaGLOaGaayzkaaGaeyizImQaciiBaiaac+gacaGGNbWa % aSbaaSqaamaalaaabaGaaGymaaqaaiaaiwdaaaaabeaakiaaisdacq % GHuhY2caWGTbGaamiEaiabgkHiTiaadIhadaahaaWcbeqaaiaaikda % aaGccqGHLjYScaaI0aGaeyi1HSTaamiEamaaCaaaleqabaGaaGOmaa % aakiabgkHiTiaad2gacaWG4bGaey4kaSIaaGinaiabgsMiJkaaicda % aaa!5CBE! {\log _{\frac{1}{5}}}\left( {mx - {x^2}} \right) \le {\log _{\frac{1}{5}}}4 \Leftrightarrow mx - {x^2} \ge 4 \Leftrightarrow {x^2} - mx + 4 \le 0\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiEamaaCa % aaleqabaGaaGOmaaaakiabgkHiTiaad2gacaWG4bGaey4kaSIaaGin % aiabgsMiJkaaicdaaaa!3ECE! {x^2} - mx + 4 \le 0\) vô nghiệm \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HSTaam % iEamaaCaaaleqabaGaaGOmaaaakiabgkHiTiaad2gacaWG4bGaey4k % aSIaaGinaiabg6da+iaaicdacaqGGaGaeyiaIiIaamiEaiabgIGiol % aadkfacqGHuhY2cqqHuoarcqGH8aapcaaIWaGaeyi1HSTaeyOeI0Ia % aGinaiabgYda8iaad2gacqGH8aapcaaI0aaaaa!5287! \Leftrightarrow {x^2} - mx + 4 > 0{\rm{ }}\forall x \in R \Leftrightarrow \Delta < 0 \Leftrightarrow - 4 < m < 4\)