giai hpt

\(\left\{{}\begin{matrix}\left|x-1\right|+\left|y-2\right|-1=0\\\left|x-1\right|+y-3=0\end{matrix}\right.\)  

̣

cho a,b,c>0 chứng minh

\(P=\dfrac{a}{\sqrt{ab+b^2}}+\dfrac{b}{\sqrt{bc+c^2}}+\dfrac{c}{\sqrt{ca+a^2}}\ge\dfrac{3\sqrt{2}}{2}\)

\(=>80=60t+40t=>t=0,8h\)

sau 0,8h chúng gặp nhau cách A \(S1=60.0,8=48km\)