Cho hàm y = f(x) có đạo hàm liên tục trên [0;5] và f(5) = 10; \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa8qCaeaaca % WG4bGabmOzayaafaWaaeWaaeaacaWG4baacaGLOaGaayzkaaGaaeiz % aiaadIhaaSqaaiaaicdaaeaacaaI1aaaniabgUIiYdGccqGH9aqpca % aIZaGaaGimaaaa!42BB! \int\limits_0^5 {xf'\left( x \right){\rm{d}}x} = 30\). Tính \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa8qCaeaaca % WGMbWaaeWaaeaacaWG4baacaGLOaGaayzkaaGaaeizaiaadIhaaSqa % aiaaicdaaeaacaaI1aaaniabgUIiYdaaaa!3F2B! \int\limits_0^5 {f\left( x \right){\rm{d}}x} \)
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Lời giải:
Báo saiĐặt \( \left\{ \begin{array}{l} u = x \Rightarrow {\rm{d}}u = {\rm{d}}x\\ {\rm{d}}v = f'\left( x \right){\rm{d}}x \Rightarrow v = f\left( x \right) \end{array} \right.\)
\(\int\limits_0^5 {x.f'\left( x \right){\rm{d}}x = \left. {\left( {x.f\left( x \right)} \right)} \right|_0^5 - \int\limits_0^5 {f\left( x \right){\rm{d}}x} \,} \)\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HSTaaG % 4maiaaicdacqGH9aqpcaaI1aGaamOzamaabmaabaGaaGynaaGaayjk % aiaawMcaaiabgkHiTmaapehabaGaamOzamaabmaabaGaamiEaaGaay % jkaiaawMcaaiaabsgacaWG4baaleaacaaIWaaabaGaaGynaaqdcqGH % RiI8aaaa!48E2! \Leftrightarrow 30 = 5f\left( 5 \right) - \int\limits_0^5 {f\left( x \right){\rm{d}}x} \)
\( \Leftrightarrow \int\limits_0^5 {f\left( x \right){\rm{d}}x} = 5f\left( 5 \right) - 30 = 20\)