Cho hàm số y = f(x) liên tục và có đạo hàm trên R thỏa mãn \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGynaiaadA % gadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGHsislcaaI3aGaamOz % amaabmaabaGaaGymaiabgkHiTiaadIhaaiaawIcacaGLPaaacqGH9a % qpcaaIZaWaaeWaaeaacaWG4bWaaWbaaSqabeaacaaIYaaaaOGaeyOe % I0IaaGOmaiaadIhaaiaawIcacaGLPaaacaGGSaGaeyiaIiIaamiEai % abgIGiolabl2riHcaa!4E3D! 5f\left( x \right) - 7f\left( {1 - x} \right) = 3\left( {{x^2} - 2x} \right),\forall x \in R\). Biết rằng tích phân \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamysaiabg2 % da9maapehabaGaamiEaiaac6caceWGMbGbauaadaqadaqaaiaadIha % aiaawIcacaGLPaaacaWGKbGaamiEaaWcbaGaaGimaaqaaiaaigdaa0 % Gaey4kIipakiabg2da9iabgkHiTmaalaaabaGaamyyaaqaaiaadkga % aaaaaa!4691! I = \int\limits_0^1 {x.f'\left( x \right)dx} = - \frac{a}{b}\) (với \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaaca % WGHbaabaGaamOyaaaaaaa!37D0! \frac{a}{b}\) là phân số tối giản). Tính T = 2a + b
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Lời giải:
Báo saiĐặt \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe % qaaiaadwhacqGH9aqpcaWG4baabaGaamizaiaadAhacqGH9aqpceWG % MbGbauaadaqadaqaaiaadIhaaiaawIcacaGLPaaacaWGKbGaamiEaa % aacaGL7baacqGHuhY2daGabaabaeqabaGaamizaiaadwhacqGH9aqp % caWGKbGaamiEaaqaaiaadAhacqGH9aqpcaWGMbWaaeWaaeaacaWG4b % aacaGLOaGaayzkaaaaaiaawUhaaiabgkDiElaadMeacqGH9aqpcaWG % 4bGaaiOlaiaadAgadaqadaqaaiaadIhaaiaawIcacaGLPaaadaabba % qaauaabeqaceaaaeaacaaIXaaabaGaaGimaaaaaiaawEa7aiabgkHi % TmaapehabaGaamOzamaabmaabaGaamiEaaGaayjkaiaawMcaaiaads % gacaWG4bGaeyypa0JaamOzamaabmaabaGaaGymaaGaayjkaiaawMca % aiabgkHiTaWcbaGaaGimaaqaaiaaigdaa0Gaey4kIipakmaapehaba % GaamOzamaabmaabaGaamiEaaGaayjkaiaawMcaaiaadsgacaWG4baa % leaacaaIWaaabaGaaGymaaqdcqGHRiI8aaaa!7506! \left\{ \begin{array}{l} u = x\\ dv = f'\left( x \right)dx \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} du = dx\\ v = f\left( x \right) \end{array} \right. \Rightarrow I = x.f\left( x \right)\left| {\begin{array}{*{20}{c}} 1\\ 0 \end{array}} \right. - \int\limits_0^1 {f\left( x \right)dx = f\left( 1 \right) - } \int\limits_0^1 {f\left( x \right)dx} \)
Thay \(% MathType!MTEF!2!1!+-
% feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9
% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x
% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe
% qaaiaadIhacqGH9aqpcaaIXaaabaGaamiEaiabg2da9iaaicdaaaGa
% ay5Eaaaaaa!3C8F!
\left\{ \begin{array}{l}
x = 1\\
x = 0
\end{array} \right.\) vào giả thiết, ta được \(% MathType!MTEF!2!1!+-
% feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9
% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x
% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe
% qaaiaaiwdacaWGMbWaaeWaaeaacaaIWaaacaGLOaGaayzkaaGaeyOe
% I0IaaG4naiaadAgadaqadaqaaiaaigdaaiaawIcacaGLPaaacqGH9a
% qpcaaIWaaabaGaeyOeI0IaaG4naiaadAgadaqadaqaaiaaicdaaiaa
% wIcacaGLPaaacqGHRaWkcaaI1aGaamOzamaabmaabaGaaGymaaGaay
% jkaiaawMcaaiabg2da9iabgkHiTiaaiodaaaGaay5EaaGaeyi1HS9a
% aiqaaqaabeqaaiaadAgadaqadaqaaiaaicdaaiaawIcacaGLPaaacq
% GH9aqpdaWcaaqaaiaaiEdaaeaacaaI4aaaaaqaaiaadAgadaqadaqa
% aiaaigdaaiaawIcacaGLPaaacqGH9aqpdaWcaaqaaiaaiwdaaeaaca
% aI4aaaaaaacaGL7baaaaa!5D04!
\left\{ \begin{array}{l}
5f\left( 0 \right) - 7f\left( 1 \right) = 0\\
- 7f\left( 0 \right) + 5f\left( 1 \right) = - 3
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
f\left( 0 \right) = \frac{7}{8}\\
f\left( 1 \right) = \frac{5}{8}
\end{array} \right.\).
Ta có \(% MathType!MTEF!2!1!+-
% feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn
% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr
% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9
% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x
% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa8qCaeaaca
% aI1aGaamOzamaabmaabaGaamiEaaGaayjkaiaawMcaaiaadsgacaWG
% 4baaleaacaaIWaaabaGaaGymaaqdcqGHRiI8aOGaeyOeI0Yaa8qCae
% aacaaI3aGaamOzamaabmaabaGaaGymaiabgkHiTiaadIhaaiaawIca
% caGLPaaacaWGKbGaamiEaaWcbaGaaGimaaqaaiaaigdaa0Gaey4kIi
% pakiabg2da9maapehabaGaaG4mamaabmaabaGaamiEamaaCaaaleqa
% baGaaGOmaaaakiabgkHiTiaaikdacaWG4baacaGLOaGaayzkaaGaam
% izaiaadIhaaSqaaiaaicdaaeaacaaIXaaaniabgUIiYdGccqGHshI3
% cqGHsislcaaIYaWaa8qCaeaacaWGMbWaaeWaaeaacaWG4baacaGLOa
% GaayzkaaGaamizaiaadIhaaSqaaiaaicdaaeaacaaIXaaaniabgUIi
% YdGccqGH9aqpcqGHsislcaaIYaGaeyO0H49aa8qCaeaacaWGMbWaae
% WaaeaacaWG4baacaGLOaGaayzkaaGaamizaiaadIhaaSqaaiaaicda
% aeaacaaIXaaaniabgUIiYdGccqGH9aqpcaaIXaaaaa!7787!
\int\limits_0^1 {5f\left( x \right)dx} - \int\limits_0^1 {7f\left( {1 - x} \right)dx} = \int\limits_0^1 {3\left( {{x^2} - 2x} \right)dx} \Rightarrow - 2\int\limits_0^1 {f\left( x \right)dx} = - 2 \Rightarrow \int\limits_0^1 {f\left( x \right)dx} = 1\).
Do đó . \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamysaiabg2 % da9iaadAgadaqadaqaaiaaigdaaiaawIcacaGLPaaacqGHsislcaaI % XaGaeyypa0ZaaSaaaeaacaaI1aaabaGaaGioaaaacqGHsislcaaIXa % Gaeyypa0JaeyOeI0YaaSaaaeaacaaIZaaabaGaaGioaaaadaGdKaWc % baaabeGccaGLsgcacaWGHbGaeyypa0JaaG4maiaacUdacaWGIbGaey % ypa0JaaGioaiabgkDiElaadsfacqGH9aqpcaaIXaGaaGinaaaa!51C3! I = f\left( 1 \right) - 1 = \frac{5}{8} - 1 = - \frac{3}{8}a = 3;b = 8 \Rightarrow T = 14\)
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 5