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Câu hỏi: Cho hàm số $f\left( x \right)=\cos 3x$. Mệnh đề nào sau đây đúng
A. $\int{f\left( x \right)\text{d}x=\dfrac{1}{3}\sin 3x+C}$.
B. $\int{f\left( x \right)\text{d}x=-\dfrac{1}{3}\sin 3x+C}$.
C. $\int{f\left( x \right)\text{d}x=3\sin 3x+C}$.
D. $\int{f\left( x \right)\text{d}x=-3\sin 3x+C}$.
A. $\int{f\left( x \right)\text{d}x=\dfrac{1}{3}\sin 3x+C}$.
B. $\int{f\left( x \right)\text{d}x=-\dfrac{1}{3}\sin 3x+C}$.
C. $\int{f\left( x \right)\text{d}x=3\sin 3x+C}$.
D. $\int{f\left( x \right)\text{d}x=-3\sin 3x+C}$.
$\int{\cos 3x\text{d}x}$ $=\int{\cos 3x\text{d}\left( \text{3}x \right)}$ $=\dfrac{1}{3}\sin 3x+C$.
Đáp án A.
