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Câu hỏi: Nguyên hàm của hàm số $f\left( x \right)=\sin x.cos 2x$ là
A. $\int{f\left( x \right)dx}=\dfrac{1}{6}\cos 3x-\dfrac{1}{2}\sin x+C$
B. $\int{f\left( x \right)dx}=\dfrac{1}{6}\cos 3x+\dfrac{1}{2}\sin x+C$
C. $\int{f\left( x \right)dx}=\dfrac{{{\cos }^{3}}x}{3}+\cos x+C$
D. $\int{f\left( x \right)dx}=\dfrac{-2{{\cos }^{3}}x}{3}+\cos x+C$
A. $\int{f\left( x \right)dx}=\dfrac{1}{6}\cos 3x-\dfrac{1}{2}\sin x+C$
B. $\int{f\left( x \right)dx}=\dfrac{1}{6}\cos 3x+\dfrac{1}{2}\sin x+C$
C. $\int{f\left( x \right)dx}=\dfrac{{{\cos }^{3}}x}{3}+\cos x+C$
D. $\int{f\left( x \right)dx}=\dfrac{-2{{\cos }^{3}}x}{3}+\cos x+C$
$\int{\sin x.cos}2xdx=\int{\left( 2{{\cos }^{2}}x-1 \right)\sin xdx=-\int{\left( 2{{\cos }^{2}}x-1 \right)d\left( \cos x \right)=\dfrac{-2{{\cos }^{3}}x}{3}+\cos x+C}}$
Đáp án D.