Cho hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9iaadAgacaGGOaGaamiEaiaacMcacqGH9aqpdaWcaaqaaiGacoga % caGGVbGaai4CamaaCaaaleqabaGaaGOmaaaakiaadIhaaeaacaaIXa % Gaey4kaSIaci4CaiaacMgacaGGUbWaaWbaaSqabeaacaaIYaaaaOGa % amiEaaaaaaa!4777! y = f(x) = \frac{{{{\cos }^2}x}}{{1 + {{\sin }^2}x}}\). Giá trị \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaWaaSaaaeaacqaHapaCaeaacaaI0aaaaaGaayjkaiaawMcaaiab % gkHiTiaaiodaceWGMbGbauaadaqadaqaamaalaaabaGaeqiWdahaba % GaaGinaaaaaiaawIcacaGLPaaaaaa!41A8! f\left( {\frac{\pi }{4}} \right) - 3f'\left( {\frac{\pi }{4}} \right)\) là:
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOzayaafa % WaaeWaaeaacaWG4baacaGLOaGaayzkaaGaeyypa0ZaaSaaaeaacqGH % sislcaaIYaGaci4yaiaac+gacaGGZbGaamiEaiGacohacaGGPbGaai % OBaiaadIhadaqadaqaaiaaigdacqGHRaWkciGGZbGaaiyAaiaac6ga % daahaaWcbeqaaiaaikdaaaGccaWG4baacaGLOaGaayzkaaGaeyOeI0 % IaaGOmaiGacogacaGGVbGaai4CaiaadIhaciGGZbGaaiyAaiaac6ga % caWG4bGaci4yaiaac+gacaGGZbWaaWbaaSqabeaacaaIYaaaaOGaam % iEaaqaamaabmaabaGaaGymaiabgUcaRiGacohacaGGPbGaaiOBamaa % CaaaleqabaGaaGOmaaaakiaadIhaaiaawIcacaGLPaaadaahaaWcbe % qaaiaaikdaaaaaaaaa!62AB! f'\left( x \right) = \frac{{ - 2\cos x\sin x\left( {1 + {{\sin }^2}x} \right) - 2\cos x\sin x{{\cos }^2}x}}{{{{\left( {1 + {{\sin }^2}x} \right)}^2}}}\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyypa0ZaaS % aaaeaacqGHsislcaaIYaGaci4yaiaac+gacaGGZbGaamiEaiGacoha % caGGPbGaaiOBaiaadIhadaqadaqaaiaaigdacqGHRaWkciGGZbGaai % yAaiaac6gadaahaaWcbeqaaiaaikdaaaGccaWG4bGaey4kaSIaci4y % aiaac+gacaGGZbWaaWbaaSqabeaacaaIYaaaaOGaamiEaaGaayjkai % aawMcaaaqaamaabmaabaGaaGymaiabgUcaRiGacohacaGGPbGaaiOB % amaaCaaaleqabaGaaGOmaaaakiaadIhaaiaawIcacaGLPaaadaahaa % WcbeqaaiaaikdaaaaaaOGaeyypa0ZaaSaaaeaacqGHsislcaaI0aGa % ci4yaiaac+gacaGGZbGaamiEaiGacohacaGGPbGaaiOBaiaadIhaae % aadaqadaqaaiaaigdacqGHRaWkciGGZbGaaiyAaiaac6gadaahaaWc % beqaaiaaikdaaaGccaWG4baacaGLOaGaayzkaaWaaWbaaSqabeaaca % aIYaaaaaaaaaa!6A09! = \frac{{ - 2\cos x\sin x\left( {1 + {{\sin }^2}x + {{\cos }^2}x} \right)}}{{{{\left( {1 + {{\sin }^2}x} \right)}^2}}} = \frac{{ - 4\cos x\sin x}}{{{{\left( {1 + {{\sin }^2}x} \right)}^2}}}\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzamaabm % aabaWaaSaaaeaacqaHapaCaeaacaaI0aaaaaGaayjkaiaawMcaaiab % gkHiTiaaiodaceWGMbGbauaadaqadaqaamaalaaabaGaeqiWdahaba % GaaGinaaaaaiaawIcacaGLPaaacqGH9aqpdaWcaaqaaiaaigdaaeaa % caaIZaaaaiabgUcaRmaalaaabaGaaGioaaqaaiaaiodaaaGaeyypa0 % JaaG4maaaa!486A! f\left( {\frac{\pi }{4}} \right) - 3f'\left( {\frac{\pi }{4}} \right) = \frac{1}{3} + \frac{8}{3} = 3\)