Tìm tất cả các giá trị thực của tham số m để phương trình \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaaiaaikdaaeqaaOWaaeWaaeaacaWGTbGaamiE % aiabgkHiTiaadIhadaahaaWcbeqaaiaaikdaaaaakiaawIcacaGLPa % aacqGH9aqpcaaIYaaaaa!41CD! {\log _2}\left( {mx - {x^2}} \right) = 2\) vô nghiệm?
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciiBaiaac+ % gacaGGNbWaaSbaaSqaaiaaikdaaeqaaOWaaeWaaeaacaWGTbGaamiE % aiabgkHiTiaadIhadaahaaWcbeqaaiaaikdaaaaakiaawIcacaGLPa % aacqGH9aqpcaaIYaGaeyi1HSTaeyOeI0IaamiEamaaCaaaleqabaGa % aGOmaaaakiabgUcaRiaad2gacaWG4bGaeyOeI0IaaGinaiabg2da9i % aaicdacaGGOaGaaiOkaiaacMcaaaa!4F49! {\log _2}\left( {mx - {x^2}} \right) = 2 \Leftrightarrow - {x^2} + mx - 4 = 0(*)\)
Phương trình (*) vô nghiệm \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HSTaeu % iLdqKaeyipaWJaaGimaiabgsDiBlaad2gadaahaaWcbeqaaiaaikda % aaGccqGHsislcaaIXaGaaGOnaiabgYda8iaaicdacqGHuhY2cqGHsi % slcaaI0aGaeyipaWJaamyBaiabgYda8iaaisdaaaa!4B9A! \Leftrightarrow \Delta < 0 \Leftrightarrow {m^2} - 16 < 0 \Leftrightarrow - 4 < m < 4\)