Bài 21:
a) Ta có: \(\left|x-5\right|=3\)
\(\Leftrightarrow\left[{}\begin{matrix}x-5=3\\x-5=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=8\\x=2\end{matrix}\right.\)
b) Ta có: \(\left|-5x\right|=3x-16\)
\(\Leftrightarrow\left[{}\begin{matrix}-5x=3x-16\left(x\le0\right)\\5x=3x-16\left(x>0\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-5x-3x=-16\\5x-3x=-16\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}-8x=-16\\2x=-16\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\left(loại\right)\\x=-8\left(loại\right)\end{matrix}\right.\)
c) Ta có: \(\left|x-4\right|=-3x+5\)
\(\Leftrightarrow\left[{}\begin{matrix}x-4=-3x+5\left(x\ge4\right)\\x-4=3x-5\left(x< 4\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x+3x=5+4\\x-3x=-5+4\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}4x=9\\-2x=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{9}{4}\left(loại\right)\\x=\dfrac{1}{2}\left(nhận\right)\end{matrix}\right.\)
d) Ta có: \(\left|3x-1\right|-x=2\)
\(\Leftrightarrow\left|3x-1\right|=2-x\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-1=2-x\left(x\ge\dfrac{1}{3}\right)\\3x-1=x-2\left(x< \dfrac{1}{3}\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x+x=2+1\\3x-x=-2+1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}4x=3\\2x=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{4}\left(nhận\right)\\x=\dfrac{-1}{2}\left(nhận\right)\end{matrix}\right.\)
27-34 ạ giúp mik với mik cám ơn nhiều
