Biết tích phân0^1 f( x ) + 2x dx = 3 . Khi đó tích phân 0^1 f( x )dx bằng

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Biết \[\int\limits_0^1 {\left[ {f\left( x \right) + 2x} \right]} dx = 3\]. Khi đó \[\int\limits_0^1 {f\left( x \right){\rm{d}}x} \] bằng

\(1\).

\(5\).

\(3\).

\(2\).

Giải thích

Chọn D

Ta có \(\int\limits_0^1 {\left[ {f\left( x \right) + 2x} \right]} dx = 3 \Leftrightarrow \int\limits_0^1 {f\left( x \right)} dx + 2\int\limits_0^1 x dx = 3 \Leftrightarrow \int\limits_0^1 {f\left( x \right)} dx + 2.\frac{{{x^2}}}{2}\left| {\begin{array}{*{20}{c}}1\\0\end{array}} \right. = 3\).

Suy ra \(\int\limits_0^1 {f\left( x \right){\rm{d}}x} = 3 - {x^2}\left| {\begin{array}{*{20}{c}}1\\0\end{array}} \right. = 3 - \left( {1 - 0} \right) = 2\).