Cho hàm số f(x) có đạo hàm \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzaiaacE % cadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpdaqadaqaaiaa % dIhadaahaaWcbeqaaiaaikdaaaGccqGHRaWkcaWG4baacaGLOaGaay % zkaaWaaeWaaeaacaWG4bGaeyOeI0IaaGOmaaGaayjkaiaawMcaamaa % CaaaleqabaGaaGOmaaaakmaabmaabaGaaGOmamaaCaaaleqabaGaam % iEaaaakiabgkHiTiaaisdaaiaawIcacaGLPaaacaGGSaGaeyiaIiIa % amiEaiabgIGiolabl2riHcaa!5025! f'\left( x \right) = \left( {{x^2} + x} \right){\left( {x - 2} \right)^2}\left( {{2^x} - 4} \right),\forall x \in \)R. Số điểm cực trị của f(x) là:
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Lời giải:
Báo saiTa có:\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzaiaacE % cadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpcaaIWaaaaa!3BD0! f'\left( x \right) = 0\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacqGHuh % Y2daqadaqaaiaadIhadaahaaWcbeqaaiaaikdaaaGccqGHRaWkcaWG % 4baacaGLOaGaayzkaaWaaeWaaeaacaWG4bGaeyOeI0IaaGOmaaGaay % jkaiaawMcaamaaCaaaleqabaGaaGOmaaaakmaabmaabaGaaGOmamaa % CaaaleqabaGaamiEaaaakiabgkHiTiaaisdaaiaawIcacaGLPaaacq % GH9aqpcaaIWaaabaGaeyi1HSTaamiEamaabmaabaGaamiEaiabgUca % RiaaigdaaiaawIcacaGLPaaadaqadaqaaiaadIhacqGHsislcaaIYa % aacaGLOaGaayzkaaWaaWbaaSqabeaacaaIYaaaaOWaaeWaaeaacaaI % YaWaaWbaaSqabeaacaWG4baaaOGaeyOeI0IaaGOmamaaCaaaleqaba % GaaGOmaaaaaOGaayjkaiaawMcaaiabg2da9iaaicdaaeaacqGHuhY2 % daWabaabaeqabaGaamiEaiabg2da9iaaicdaaeaacaWG4bGaey4kaS % IaaGymaiabg2da9iaaicdaaeaacaWG4bGaeyOeI0IaaGOmaiabg2da % 9iaaicdaaeaacaaIYaWaaWbaaSqabeaacaWG4baaaOGaeyOeI0IaaG % OmamaaCaaaleqabaGaaGOmaaaakiabg2da9iaaicdaaaGaay5waaGa % eyi1HS9aamqaaqaabeqaaiaadIhacqGH9aqpcaaIWaaabaGaamiEai % abg2da9iabgkHiTiaaigdaaeaacaWG4bGaeyypa0JaaGOmaaqaaiaa % dIhacqGH9aqpcaaIYaaaaiaawUfaaiabgsDiBpaadeaaeaqabeaaca % WG4bGaeyypa0JaaGimaiaaykW7caaMc8UaaiikaiaackgacaGGVbGa % aiyAaiaaykW7caaMc8UaaGymaiaacMcaaeaacaWG4bGaeyypa0Jaey % OeI0IaaGymaiaaykW7caaMc8UaaiikaiaackgacaGGVbGaaiyAaiaa % ykW7caaMc8UaaGymaiaacMcaaeaacaWG4bGaeyypa0JaaGOmaiaayk % W7caaMc8UaaiikaiaackgacaGGVbGaaiyAaiaaykW7caaMc8UaaG4m % aiaacMcaaaGaay5waaaaaaa!B032! \begin{array}{l} \Leftrightarrow \left( {{x^2} + x} \right){\left( {x - 2} \right)^2}\left( {{2^x} - 4} \right) = 0\\ \Leftrightarrow x\left( {x + 1} \right){\left( {x - 2} \right)^2}\left( {{2^x} - {2^2}} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l} x = 0\\ x + 1 = 0\\ x - 2 = 0\\ {2^x} - {2^2} = 0 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} x = 0\\ x = - 1\\ x = 2\\ x = 2 \end{array} \right. \Leftrightarrow \left[ \begin{array}{l} x = 0\,\,(bội\,\,1)\\ x = - 1\,\,(bội\,\,1)\\ x = 2\,\,(bội\,\,3) \end{array} \right. \end{array}\)
Ta thấy phương trình f'(x) = 0 có 3 nghiệm phân biệt và các nghiệm này đều là nghiệm bội lẻ nên hàm số y = f(x) có 3 điểm cực trị.
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 4