ĐKXĐ:.
a. \(\left\{{}\begin{matrix}cosx\ne0\\sin3x\ne0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ne\dfrac{\pi}{2}+k2\pi\\x\ne\dfrac{k\pi}{3}\end{matrix}\right.\)
b. \(-1\le cosx\Rightarrow1+cosx\ge0\) ; \(\forall x\)
Hay hàm xác định trên R
c. \(cosx-cos3x\ne0\)
\(\Leftrightarrow cos3x\ne cosx\)
\(\Leftrightarrow\left[{}\begin{matrix}3x\ne x+k2\pi\\3x\ne-x+k2\pi\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x\ne k\pi\\x\ne\dfrac{k\pi}{2}\end{matrix}\right.\) \(\Leftrightarrow x\ne\dfrac{k\pi}{2}\)
Đúng 1
Bình luận (0)
