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Câu hỏi: Tìm nguyên hàm của hàm số $f(x)=\dfrac{1}{{{\sin }^{2}}\left( x+\dfrac{\pi }{3} \right)}$.
A. $\int{f(x)dx=-\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
B. $\int{f(x)dx=-\dfrac{1}{3}\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
C. $\int{f(x)dx=\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
D. $\int{f(x)dx=\dfrac{1}{3}\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
A. $\int{f(x)dx=-\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
B. $\int{f(x)dx=-\dfrac{1}{3}\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
C. $\int{f(x)dx=\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
D. $\int{f(x)dx=\dfrac{1}{3}\cot \left( x+\dfrac{\pi }{3} \right)}+C.$
$\int{\dfrac{dx}{{{\sin }^{2}}\left( x+\dfrac{\pi }{3} \right)}=}\int{\dfrac{d\left( x+\dfrac{\pi }{3} \right)}{{{\sin }^{2}}\left( x+\dfrac{\pi }{3} \right)}=-\cot }\left( x+\dfrac{\pi }{3} \right)+C$.
Đáp án A.