Hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9iaadAgadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpdaWc % aaqaaiaaikdaaeaaciGGJbGaai4Baiaacohadaqadaqaaiabec8aWj % aadIhaaiaawIcacaGLPaaaaaaaaa!4451! y = f\left( x \right) = \frac{2}{{\cos \left( {\pi x} \right)}}\) có f'(3) bằng:
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzaiaacE % cadaqadaqaaiaadIhaaiaawIcacaGLPaaacqGH9aqpdaWcaaqaaiaa % ikdaaeaaciGGJbGaai4Baiaacohadaqadaqaaiabec8aWjaadIhaai % aawIcacaGLPaaaaaGaeyypa0JaaGOmaiaac6cadaqadaqaaiGacoga % caGGVbGaai4CamaabmaabaGaeqiWdaNaamiEaaGaayjkaiaawMcaaa % GaayjkaiaawMcaaiaacEcacaGGUaWaaSaaaeaacqGHsislcaaIXaaa % baGaci4yaiaac+gacaGGZbWaaWbaaSqabeaacaaIYaaaaOWaaeWaae % aacqaHapaCcaWG4baacaGLOaGaayzkaaaaaiabg2da9iaaikdacaGG % UaGaeqiWda3aaSaaaeaaciGGZbGaaiyAaiaac6gadaqadaqaaiabec % 8aWjaadIhaaiaawIcacaGLPaaaaeaaciGGJbGaai4Baiaacohadaah % aaWcbeqaaiaaikdaaaGcdaqadaqaaiabec8aWjaadIhaaiaawIcaca % GLPaaaaaaaaa!6C8E! f'\left( x \right) = \frac{2}{{\cos \left( {\pi x} \right)}} = 2.\left( {\cos \left( {\pi x} \right)} \right)'.\frac{{ - 1}}{{{{\cos }^2}\left( {\pi x} \right)}} = 2.\pi \frac{{\sin \left( {\pi x} \right)}}{{{{\cos }^2}\left( {\pi x} \right)}}\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOzaiaacE % cadaqadaqaaiaaiodaaiaawIcacaGLPaaacqGH9aqpcaaIYaGaeqiW % daNaaiOlamaalaaabaGaci4CaiaacMgacaGGUbGaaG4maiabec8aWb % qaaiGacogacaGGVbGaai4CamaaCaaaleqabaGaaGOmaaaakiaaioda % cqaHapaCaaGaeyypa0JaaGimaaaa!4B63! f'\left( 3 \right) = 2\pi .\frac{{\sin 3\pi }}{{{{\cos }^2}3\pi }} = 0\)
