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Câu hỏi: Nếu $\int{f\left( x \right)}\text{d}x=4{{x}^{3}}+{{x}^{2}}+C$ thì hàm số $f\left( x \right)$ bằng
A. $f\left( x \right)={{x}^{4}}+\dfrac{{{x}^{3}}}{3}+Cx$.
B. $f\left( x \right)=12{{x}^{2}}+2x+C$.
C. $f\left( x \right)=12{{x}^{2}}+2x$.
D. $f\left( x \right)={{x}^{4}}+\dfrac{{{x}^{3}}}{3}$.
A. $f\left( x \right)={{x}^{4}}+\dfrac{{{x}^{3}}}{3}+Cx$.
B. $f\left( x \right)=12{{x}^{2}}+2x+C$.
C. $f\left( x \right)=12{{x}^{2}}+2x$.
D. $f\left( x \right)={{x}^{4}}+\dfrac{{{x}^{3}}}{3}$.
Ta có: $f\left( x \right)={{\left( \int{f\left( x \right)}\text{d}x \right)}^{\prime }}={{\left( 4{{x}^{3}}+{{x}^{2}}+C \right)}^{\prime }}=12{{x}^{2}}+2x$.
Đáp án C.