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Câu hỏi: Họ các nguyên hàm của hàm số $f\left( x \right)=\text{sin}21x$ là
A. $\int{f\left( x \right)\text{d}x}=21\text{cos}21x+C$
B. $\int{f\left( x \right)\text{d}x}=\dfrac{1}{21}\text{cos}21x+C$
C. $\int{f\left( x \right)\text{d}x}=-21\text{cos}21x+C$
D. $\int{f\left( x \right)\text{d}x}=-\dfrac{1}{21}\text{cos}21x+C$
A. $\int{f\left( x \right)\text{d}x}=21\text{cos}21x+C$
B. $\int{f\left( x \right)\text{d}x}=\dfrac{1}{21}\text{cos}21x+C$
C. $\int{f\left( x \right)\text{d}x}=-21\text{cos}21x+C$
D. $\int{f\left( x \right)\text{d}x}=-\dfrac{1}{21}\text{cos}21x+C$
Ta có $\int{f\left( x \right)\text{d}x}=\int{\text{sin}21x\text{d}x}=-\dfrac{1}{21}\text{cos}21x+C$.
Đáp án D.