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Câu hỏi: Cho hàm số $f\left( x \right)=4x+\sin 3x$. Khẳng định nào dưới đây đúng?
A. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}+\dfrac{\cos 3x}{3}+C.$
B. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}+\dfrac{\sin 3x}{3}+C.$
C. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}-\dfrac{\cos 3x}{3}+C.$
D. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}-\dfrac{\sin 3x}{3}+C.$
A. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}+\dfrac{\cos 3x}{3}+C.$
B. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}+\dfrac{\sin 3x}{3}+C.$
C. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}-\dfrac{\cos 3x}{3}+C.$
D. $\int{f\left( x \right)\text{d}x}=2{{x}^{2}}-\dfrac{\sin 3x}{3}+C.$
Ta có $\int{f\left( x \right)\text{d}x}=\int{\left[ 4x+\sin 3x \right]\text{d}x}=2{{x}^{2}}-\dfrac{\cos 3x}{3}+C.$
Đáp án C.