Cho hàm số bậc bốn \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9iaadAgadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpcaWG % HbGaamiEamaaCaaaleqabaGaaGinaaaakiabgUcaRiaadkgacaWG4b % WaaWbaaSqabeaacaaIZaaaaOGaey4kaSIaam4yaiaadIhadaahaaWc % beqaaiaaikdaaaGccqGHRaWkcaWGKbGaamiEaiabgUcaRiaadwgaaa % a!4B4E! y = f\left( x \right) = a{x^4} + b{x^3} + c{x^2} + dx + e\) có đồ thị f'(x) như hình vẽ. Phương trình \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9iaaikdacaWGHbGaey4k % aSIaamOyaiabgUcaRiaadogacqGHRaWkcaWGKbGaey4kaSIaamyzaa % aa!4336! f\left( x \right) = 2a + b + c + d + e\) có số nghiệm là
Hãy suy nghĩ và trả lời câu hỏi trước khi xem đáp án
Lời giải:
Báo saiTa có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOzayaafa % WaaeWaaeaacaWG4baacaGLOaGaayzkaaGaeyypa0JaaGinaiaadgga % caWG4bGaaiOlamaabmaabaGaamiEaiabgkHiTiaaigdaaiaawIcaca % GLPaaadaqadaqaaiaadIhacqGHsislcaaIYaaacaGLOaGaayzkaaGa % eyypa0JaaGinaiaadggacaWG4bWaaWbaaSqabeaacaaIZaaaaOGaey % OeI0IaaGymaiaaikdacaWGHbGaamiEamaaCaaaleqabaGaaGOmaaaa % kiabgUcaRiaaiIdacaWGHbGaamiEaaaa!5382! f'\left( x \right) = 4ax.\left( {x - 1} \right)\left( {x - 2} \right) = 4a{x^3} - 12a{x^2} + 8ax\)
Suy ra \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9maapeaabaGabmOzayaa % faWaaeWaaeaacaWG4baacaGLOaGaayzkaaGaamizaiaadIhaaSqabe % qaniabgUIiYdGccqGH9aqpcaWGHbGaamiEamaaCaaaleqabaGaaGin % aaaakiabgkHiTiaaisdacaWGHbGaamiEamaaCaaaleqabaGaaG4maa % aakiabgUcaRiaaisdacaWGHbGaamiEamaaCaaaleqabaGaaGOmaaaa % kiabgUcaRiaadwgacqGHshI3caWGIbGaeyypa0JaeyOeI0IaaGinai % aadggacaGG7aGaam4yaiabg2da9iaaisdacaWGHbGaai4oaiaadsga % cqGH9aqpcaaIWaaaaa!5F08! f\left( x \right) = \int {f'\left( x \right)dx} = a{x^4} - 4a{x^3} + 4a{x^2} + e \Rightarrow b = - 4a;c = 4a;d = 0\)
Vậy \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9iaaikdacaWGHbGaey4k % aSIaamOyaiabgUcaRiaadogacqGHRaWkcaWGKbGaey4kaSIaamyzai % abg2da9iaaikdacaWGHbGaey4kaSIaamyzaiabgsDiBlaadggacaWG % 4bWaaWbaaSqabeaacaaI0aaaaOGaeyOeI0IaaGinaiaadggacaWG4b % WaaWbaaSqabeaacaaIZaaaaOGaey4kaSIaaGinaiaadggacaWG4bWa % aWbaaSqabeaacaaIYaaaaOGaey4kaSIaamyzaiabg2da9iaaikdaca % WGHbGaey4kaSIaamyzaaaa!5C16! f\left( x \right) = 2a + b + c + d + e = 2a + e \Leftrightarrow a{x^4} - 4a{x^3} + 4a{x^2} + e = 2a + e\)\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HSTaam % iEamaaCaaaleqabaGaaGinaaaakiabgkHiTiaaisdacaWG4bWaaWba % aSqabeaacaaIZaaaaOGaey4kaSIaaGinaiaadIhadaahaaWcbeqaai % aaikdaaaGccqGHsislcaaIYaGaeyypa0JaaGimaiabgsDiBpaabmaa % baGaamiEamaaCaaaleqabaGaaGOmaaaakiabgkHiTiaaikdacaWG4b % aacaGLOaGaayzkaaWaaWbaaSqabeaacaaIYaaaaOGaeyOeI0YaaeWa % aeaadaGcaaqaaiaaikdaaSqabaaakiaawIcacaGLPaaadaahaaWcbe % qaaiaaikdaaaGccqGH9aqpcaaIWaGaeyi1HS9aamqaaqaabeqaaiaa % dIhadaahaaWcbeqaaiaaikdaaaGccqGHsislcaaIYaGaamiEaiabg2 % da9maakaaabaGaaGOmaaWcbeaaaOqaaiaadIhadaahaaWcbeqaaiaa % ikdaaaGccqGHsislcaaIYaGaamiEaiabg2da9iabgkHiTmaakaaaba % GaaGOmaaWcbeaaaaGccaGLBbaaaaa!6593! \Leftrightarrow {x^4} - 4{x^3} + 4{x^2} - 2 = 0 \Leftrightarrow {\left( {{x^2} - 2x} \right)^2} - {\left( {\sqrt 2 } \right)^2} = 0 \Leftrightarrow \left[ \begin{array}{l} {x^2} - 2x = \sqrt 2 \\ {x^2} - 2x = - \sqrt 2 \end{array} \right.\)
Do đó phương trình đã cho có hai nghiệm phân biệt.
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 5