Cho hàm số y = f(x) có đồ thị như hình vẽ. Trong đoạn [-20;20], có bao nhiêu số nguyên m để hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9maaemaabaGaaGymaiaaicdacaWGMbWaaeWaaeaacaWG4bGaeyOe % I0IaamyBaaGaayjkaiaawMcaaiabgkHiTmaalaaabaGaaGymaiaaig % daaeaacaaIZaaaaiaad2gadaahaaWcbeqaaiaaikdaaaGccqGHRaWk % daWcaaqaaiaaiodacaaI3aaabaGaaG4maaaacaWGTbaacaGLhWUaay % jcSdaaaa!4B12! y = \left| {10f\left( {x - m} \right) - \frac{{11}}{3}{m^2} + \frac{{37}}{3}m} \right|\)có 3 điểm cực trị?
Hãy suy nghĩ và trả lời câu hỏi trước khi xem đáp án
Lời giải:
Báo saiSố điểm cực trị của hàm số đã cho là số điểm cực trị của hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9maaemaabaGaaGymaiaaicdacaWGMbWaaeWaaeaacaWG4baacaGL % OaGaayzkaaGaeyOeI0YaaSaaaeaacaaIXaGaaGymaaqaaiaaiodaaa % GaamyBamaaCaaaleqabaGaaGOmaaaakiabgUcaRmaalaaabaGaaG4m % aiaaiEdaaeaacaaIZaaaaiaad2gaaiaawEa7caGLiWoaaaa!4933! y = \left| {10f\left( x \right) - \frac{{11}}{3}{m^2} + \frac{{37}}{3}m} \right|\).
Xét hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4zamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9iaaigdacaaIWaGaamOz % amaabmaabaGaamiEaaGaayjkaiaawMcaaiabgkHiTmaalaaabaGaaG % ymaiaaigdaaeaacaaIZaaaaiaad2gadaahaaWcbeqaaiaaikdaaaGc % cqGHRaWkdaWcaaqaaiaaiodacaaI3aaabaGaaG4maaaacaWGTbaaaa!4885! g\left( x \right) = 10f\left( x \right) - \frac{{11}}{3}{m^2} + \frac{{37}}{3}m\) thì \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabm4zayaafa % WaaeWaaeaacaWG4baacaGLOaGaayzkaaGaeyypa0JaaGymaiaaicda % ceWGMbGbauaadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpca % aIWaaaaa!4129! g'\left( x \right) = 10f'\left( x \right) = 0\) có 2 nghiệm phân biệt.
Lại có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4zamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9iaaicdacqGHuhY2caWG % MbWaaeWaaeaacaWG4baacaGLOaGaayzkaaGaeyypa0ZaaSaaaeaaca % aIXaGaaGymaaqaaiaaiodacaaIWaaaaiaad2gadaahaaWcbeqaaiaa % ikdaaaGccqGHsisldaWcaaqaaiaaiodacaaI3aaabaGaaG4maiaaic % daaaGaamyBaiaaykW7caaMc8+aaeWaaeaacaGGQaaacaGLOaGaayzk % aaaaaa!510B! g\left( x \right) = 0 \Leftrightarrow f\left( x \right) = \frac{{11}}{{30}}{m^2} - \frac{{37}}{{30}}m\,\,\left( * \right)\), để hàm số đã cho có 3 điểm cực trị thì (*) có một nghiệm đơn \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HS9aam % qaaqaabeqaamaalaaabaGaaGymaiaaigdaaeaacaaIZaGaaGimaaaa % caWGTbWaaWbaaSqabeaacaaIYaaaaOGaeyOeI0YaaSaaaeaacaaIZa % GaaG4naaqaaiaaiodacaaIWaaaaiaad2gacqGHLjYScaaIZaaabaWa % aSaaaeaacaaIXaGaaGymaaqaaiaaiodacaaIWaaaaiaad2gadaahaa % WcbeqaaiaaikdaaaGccqGHsisldaWcaaqaaiaaiodacaaI3aaabaGa % aG4maiaaicdaaaGaamyBaiabgsMiJkabgkHiTiaaigdaaaGaay5waa % Gaeyi1HS9aamqaaqaabeqaaiaad2gacqGHLjYScaaI1aaabaGaamyB % aiabgsMiJkabgkHiTmaalaaabaGaaGymaiaaiIdaaeaacaaIXaGaaG % ymaaaaaeaadaWcaaqaaiaaigdacaaI1aaabaGaaGymaiaaigdaaaGa % eyizImQaamyBaiabgsMiJkaaikdaaaGaay5waaaaaa!6842! \Leftrightarrow \left[ \begin{array}{l} \frac{{11}}{{30}}{m^2} - \frac{{37}}{{30}}m \ge 3\\ \frac{{11}}{{30}}{m^2} - \frac{{37}}{{30}}m \le - 1 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} m \ge 5\\ m \le - \frac{{18}}{{11}}\\ \frac{{15}}{{11}} \le m \le 2 \end{array} \right.\).
Kết hợp \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe % qaaiaad2gacqGHiiIZcqWIKeIOaeaacaWGTbGaeyicI48aamWaaeaa % cqGHsislcaaIYaGaaGimaiaacUdacaaIYaGaaGimaaGaay5waiaaw2 % faaaaacaGL7baacqGHshI3aaa!465F! \left\{ \begin{array}{l} m \in Z \\ m \in \left[ { - 20;20} \right] \end{array} \right. \Rightarrow \) có 36 giá trị của m
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 5