a: =>|x-3|=x+7
\(\Leftrightarrow\left\{{}\begin{matrix}x>=-7\\\left(x+7\right)^2-\left(x-3\right)^2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>=-7\\\left(x+7+x-3\right)\left(x+7-x+3\right)=0\end{matrix}\right.\)
=>x=-2
b: |x+3|=|5-x|
=>x+3=5-x hoặc x+3=x-5(loại)
=>2x=2
hay x=1