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Câu hỏi: Cho hàm số $f\left( x \right)=\sin 3x.$ Trong các khẳng định sau, khẳng định nào đúng?
A. $\int{f\left( x \right)\text{d}x}=-\dfrac{1}{3}\text{cos}3x+C$.
B. $\int{f\left( x \right)\text{d}x}=\dfrac{1}{3}\text{cos}3x+C$.
C. $\int{f\left( x \right)\text{d}x}=-\text{cos}3x+C$.
D. $\int{f\left( x \right)\text{d}x}=\text{cos}3x+C$.
A. $\int{f\left( x \right)\text{d}x}=-\dfrac{1}{3}\text{cos}3x+C$.
B. $\int{f\left( x \right)\text{d}x}=\dfrac{1}{3}\text{cos}3x+C$.
C. $\int{f\left( x \right)\text{d}x}=-\text{cos}3x+C$.
D. $\int{f\left( x \right)\text{d}x}=\text{cos}3x+C$.
Ta có: $\int{\sin 3x\text{d}x}=-\dfrac{1}{3}\text{cos}3x+C$.
Đáp án A.