Câu 1:
\(y=sin3x.cotx=sin3x.\dfrac{cosx}{sinx}\\ HSXD:sinx\ne0\\ \Leftrightarrow x\ne k\pi\\ \Leftrightarrow TXD:D=R\backslash\left\{k\pi,k\in Z\right\}\)
\(\Rightarrow\) Chọn C
Câu 2:
\(y=\dfrac{cos2x}{tanx}=cos2x:\left(\dfrac{sinx}{cosx}\right)=cos2x.\dfrac{cosx}{sinx}\\ HSXD:sinx\ne0\\ \Leftrightarrow x\ne k\pi\\ \Leftrightarrow TXD:D=R\backslash\left\{k\pi,k\in Z\right\}\)
\(\Rightarrow\) Chọn B
Câu 3:
\(y=sin\sqrt{\dfrac{1+x}{1-x}}\\ HSXD:\left\{{}\begin{matrix}1+x\ge0\\1-x>0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x\ge-1\\x< 1\end{matrix}\right.\\ \Leftrightarrow TXD:D=[-1;1)\)
\(\Rightarrow\) Chọn D
Câu 4:
\(y=cot\left(2x-\dfrac{\pi}{4}\right)=\dfrac{cos\left(2x-\dfrac{\pi}{4}\right)}{sin\left(2x-\dfrac{\pi}{4}\right)}\\ HSXD:sin\left(2x-\dfrac{\pi}{4}\right)\ne0\\ \Leftrightarrow2x-\dfrac{\pi}{4}\ne k\pi\\ \Leftrightarrow x\ne\dfrac{k\pi}{2}+\dfrac{\pi}{8}\\ \Leftrightarrow TXD:D=R\backslash\left\{\dfrac{k\pi}{2}+\dfrac{\pi}{8},k\in Z\right\}\)
\(\Rightarrow\) Chọn A
Câu 5:
\(y=\sqrt{\dfrac{sinx+2}{cosx+1}}\\ HSXD:\left\{{}\begin{matrix}\dfrac{sinx+2}{cosx+1}\ge0\\cosx+1\ne0\end{matrix}\right.\\ \Leftrightarrow cosx+1\ne0\\ \Leftrightarrow cosx\ne-1\\ \Leftrightarrow x\ne\pi+k2\pi\\ \Leftrightarrow D=R\backslash\left\{\pi+k2\pi,k\in Z\right\}\)
\(\Rightarrow\) Chọn D
Câu 6: Chọn B
. Chọn đáp án sai:
