Biết \(\int\limits_0^3 {f\left( x \right)dx = \frac{5}{3}} \) và \(\int\limits_0^4 {f\left( t \right)dt = \frac{3}{5}} \). Tính \(\int\limits_3^4 {f\left( u \right)du} \).
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Lời giải:
Báo sai\(\int\limits_0^4 {f\left( u \right){\rm{d}}u = \int\limits_0^3 {f\left( u \right){\rm{d}}u + \int\limits_3^4 {f\left( u \right){\rm{d}}u} } } \)
\(\begin{array}{l}
\Leftrightarrow \int\limits_3^4 {f\left( u \right){\rm{d}}u} = \int\limits_0^4 {f\left( u \right){\rm{d}}u - \int\limits_0^3 {f\left( u \right){\rm{d}}u} } \\
\Leftrightarrow \int\limits_3^4 {f\left( u \right){\rm{d}}u} = \int\limits_0^4 {f\left( t \right){\rm{d}}t - \int\limits_0^3 {f\left( x \right){\rm{d}}x} }
\end{array}\)
\(\Leftrightarrow \int\limits_3^4 {f\left( u \right){\rm{d}}u} = \frac{3}{5} - \frac{5}{3} = - \frac{{16}}{{15}}\)