Cho hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9maalaaabaGaamiEamaaCaaaleqabaGaaGinaaaaaOqaaiaaisda % aaGaeyOeI0YaaSaaaeaacaWGTbGaamiEamaaCaaaleqabaGaaG4maa % aaaOqaaiaaiodaaaGaey4kaSYaaSaaaeaacaWG4bWaaWbaaSqabeaa % caaIYaaaaaGcbaGaaGOmaaaacqGHsislcaWGTbGaamiEaiabgUcaRi % aaikdacaaIWaGaaGymaiaaiMdaaaa!49A4! y= \frac{{{x^4}}}{4} - \frac{{m{x^3}}}{3} + \frac{{{x^2}}}{2} - mx + 2019\) ( m là tham số). Gọi S là tập hợp tất cả các giá trị nguyên của tham sốmđể hàm đã cho đồng biến trên khoảng \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaeWaaeaaca % aI2aGaai4oaiabgUcaRiabg6HiLcGaayjkaiaawMcaaaaa!3B4E! \left( {6; + \infty } \right)\) . Tính số phần tử của S biết rằng \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaaca % WGTbaacaGLhWUaayjcSdGaeyizImQaaGOmaiaaicdacaaIYaGaaGim % aaaa!3EA8! \left| m \right| \le 2020\).
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmyEayaafa % Gaeyypa0JaamiEamaaCaaaleqabaGaaG4maaaakiabgkHiTiaad2ga % caWG4bWaaWbaaSqabeaacaaIYaaaaOGaey4kaSIaamiEaiabgkHiTi % aad2gacqGH9aqpcaWG4bWaaeWaaeaacaWG4bWaaWbaaSqabeaacaaI % YaaaaOGaey4kaSIaaGymaaGaayjkaiaawMcaaiabgkHiTiaad2gada % qadaqaaiaadIhadaahaaWcbeqaaiaaikdaaaGccqGHRaWkcaaIXaaa % caGLOaGaayzkaaGaeyypa0ZaaeWaaeaacaWG4bGaeyOeI0IaamyBaa % GaayjkaiaawMcaamaabmaabaGaamiEamaaCaaaleqabaGaaGOmaaaa % kiabgUcaRiaaigdaaiaawIcacaGLPaaacqGHLjYScaaIWaGaeyi1HS % TaamiEaiabgkHiTiaad2gacqGHLjYScaaIWaGaeyi1HSTaamiEaiab % gwMiZkaad2gaaaa!6A59! y' = {x^3} - m{x^2} + x - m = x\left( {{x^2} + 1} \right) - m\left( {{x^2} + 1} \right) = \left( {x - m} \right)\left( {{x^2} + 1} \right) \ge 0 \Leftrightarrow x - m \ge 0 \Leftrightarrow x \ge m\)
Hàm số đã cho đồng biến trên khoảng \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaeWaaeaaca % aI2aGaai4oaiabgUcaRiabg6HiLcGaayjkaiaawMcaaiabgsDiBlaa % dIhacqGHLjYScaWGTbWaaeWaaeaacqGHaiIicaWG4bGaeyicI48aae % WaaeaacaaI2aGaai4oaiabgUcaRiabg6HiLcGaayjkaiaawMcaaaGa % ayjkaiaawMcaaiabgsDiBlaad2gacqGHKjYOcaaI2aaaaa!5157! \left( {6; + \infty } \right) \Leftrightarrow x \ge m\left( {\forall x \in \left( {6; + \infty } \right)} \right) \Leftrightarrow m \le 6\).
Kết hợp \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe % qaaiaad2gacqGHiiIZcqWIKeIOaeaadaabdaqaaiaad2gaaiaawEa7 % caGLiWoacqGHKjYOcaaIYaGaaGimaiaaikdacaaIWaaaaiaawUhaai % abgsDiBpaaceaaeaqabeaacaWGTbGaeyicI4SaeSijHikabaGaamyB % aiabgIGiopaadmaabaGaeyOeI0IaaGOmaiaaicdacaaIYaGaaGimai % aacUdacaaI2aaacaGLBbGaayzxaaaaaiaawUhaaiabgkDiEdaa!573F! \left\{ \begin{array}{l} m \in Z \\ \left| m \right| \le 2020 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} m \in Z\\ m \in Z \left[ { - 2020;6} \right] \end{array} \right. \Rightarrow \) có 2027 giá trị của m
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 5