Có bao nhiêu số nguyên \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyyaiabgI % GiopaabmaabaGaeyOeI0IaaGOmaiaaicdacaaIXaGaaGyoaiaacUda % caaIYaGaaGimaiaaigdacaaI5aaacaGLOaGaayzkaaaaaa!417B! a \in \left( { - 2019;2019} \right)\) để phương trình \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaaca % aIXaaabaGaciiBaiaac6gadaqadaqaaiaadIhacqGHRaWkcaaI1aaa % caGLOaGaayzkaaaaaiabgUcaRmaalaaabaGaaGymaaqaaiaaiodada % ahaaWcbeqaaiaadIhaaaGccqGHsislcaaIXaaaaiabg2da9iaadIha % cqGHRaWkcaWGHbaaaa!45DB! \frac{1}{{\ln \left( {x + 5} \right)}} + \frac{1}{{{3^x} - 1}} = x + a\) có hai nghiệm phân biệt?
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaaca % aIXaaabaGaciiBaiaac6gadaqadaqaaiaadIhacqGHRaWkcaaI1aaa % caGLOaGaayzkaaaaaiabgUcaRmaalaaabaGaaGymaaqaaiaaiodada % ahaaWcbeqaaiaadIhaaaGccqGHsislcaaIXaaaaiabg2da9iaadIha % cqGHRaWkcaWGHbGaeyi1HSTaamOzamaabmaabaGaamiEaaGaayjkai % aawMcaaiabg2da9maalaaabaGaaGymaaqaaiGacYgacaGGUbWaaeWa % aeaacaWG4bGaey4kaSIaaGynaaGaayjkaiaawMcaaaaacqGHRaWkda % WcaaqaaiaaigdaaeaacaaIZaWaaWbaaSqabeaacaWG4baaaOGaeyOe % I0IaaGymaaaacqGHsislcaWG4bGaeyypa0JaamyyamaabmaabaGaai % OkaaGaayjkaiaawMcaaaaa!5ED7! \frac{1}{{\ln \left( {x + 5} \right)}} + \frac{1}{{{3^x} - 1}} = x + a \Leftrightarrow f\left( x \right) = \frac{1}{{\ln \left( {x + 5} \right)}} + \frac{1}{{{3^x} - 1}} - x = a\left( * \right)\)
Xét hàm số : \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaGaamiEaaGaayjkaiaawMcaaiabg2da9maalaaabaGaaGymaaqa % aiGacYgacaGGUbWaaeWaaeaacaWG4bGaey4kaSIaaGynaaGaayjkai % aawMcaaaaacqGHRaWkdaWcaaqaaiaaigdaaeaacaaIZaWaaWbaaSqa % beaacaWG4baaaOGaeyOeI0IaaGymaaaacqGHsislcaWG4baaaa!4871! f\left( x \right) = \frac{1}{{\ln \left( {x + 5} \right)}} + \frac{1}{{{3^x} - 1}} - x\)
ĐKXĐ : \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaiqaaqaabe % qaaiaadIhacqGHRaWkcaaI1aGaeyOpa4JaaGimaaqaaiGacYgacaGG % UbWaaeWaaeaacaWG4bGaey4kaSIaaGynaaGaayjkaiaawMcaaiabgc % Mi5kaaicdaaeaacaaIZaWaaWbaaSqabeaacaWG4baaaOGaeyOeI0Ia % aGymaiabgcMi5kaaicdaaaGaay5EaaGaeyi1HS9aaiqaaqaabeqaai % aadIhacqGH+aGpcqGHsislcaaI1aaabaGaamiEaiabgUcaRiaaiwda % cqGHGjsUcaaIXaaabaGaaG4mamaaCaaaleqabaGaamiEaaaakiabgc % Mi5kaaigdaaaGaay5EaaGaeyi1HS9aaiqaaqaabeqaaiaadIhacqGH % +aGpcqGHsislcaaI1aaabaGaamiEaiabgcMi5kabgkHiTiaaisdaae % aacaWG4bGaeyiyIKRaaGimaaaacaGL7baaaaa!69FA! \left\{ \begin{array}{l} x + 5 > 0\\ \ln \left( {x + 5} \right) \ne 0\\ {3^x} - 1 \ne 0 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} x > - 5\\ x + 5 \ne 1\\ {3^x} \ne 1 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} x > - 5\\ x \ne - 4\\ x \ne 0 \end{array} \right.\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H4Taam % iraiabg2da9maabmaabaGaeyOeI0IaaGynaiaacUdacqGHsislcaaI % 0aaacaGLOaGaayzkaaGaeyOkIG8aaeWaaeaacqGHsislcaaI0aGaai % 4oaiaaicdaaiaawIcacaGLPaaacqGHQicYdaqadaqaaiaaicdacaGG % 7aGaey4kaSIaeyOhIukacaGLOaGaayzkaaaaaa!4D01! \Rightarrow D = \left( { - 5; - 4} \right) \cup \left( { - 4;0} \right) \cup \left( {0; + \infty } \right)\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzaiaacE % cadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpdaWcaaqaaiab % gkHiTiaaigdaaeaaciGGSbGaaiOBamaaCaaaleqabaGaaGOmaaaakm % aabmaabaGaamiEaiabgUcaRiaaiwdaaiaawIcacaGLPaaaaaGaeyOe % I0YaaSaaaeaacaaIZaWaaWbaaSqabeaacaWG4baaaaGcbaWaaeWaae % aacaaIZaWaaWbaaSqabeaacaWG4baaaOGaeyOeI0IaaGymaaGaayjk % aiaawMcaamaaCaaaleqabaGaaGOmaaaaaaGccqGHsislcaaIXaGaey % ipaWJaaGimaiabgcGiIiaadIhacqGHiiIZcaWGebaaaa!544F! f'\left( x \right) = \frac{{ - 1}}{{{{\ln }^2}\left( {x + 5} \right)}} - \frac{{{3^x}}}{{{{\left( {{3^x} - 1} \right)}^2}}} - 1 < 0\forall x \in D\)
BBT :
Từ BBT suy ra phương trình (*) có 2 nghiệm \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HSTaam % yyaiabgwMiZkaaisdaaaa!3BBA! \Leftrightarrow a \ge 4\)
Kết hợp ĐK \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H4Taam % yyaiabgIGiopaacmaabaGaaGinaiaacUdacaGGUaGaaiOlaiaac6ca % caGG7aGaaGOmaiaaicdacaaIXaGaaGioaaGaay5Eaiaaw2haaaaa!4431! \Rightarrow a \in \left\{ {4;...;2018} \right\}\). Vậy có 2015 giá trị của a thỏa mãn.
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 4