Ta có:\(C=\left|2x-7\right|+\left|2x-5\right|=-18\)

\(\left\{{}\begin{matrix}\left|2x-7\right|>0\\\left|2x-5\right|>0\end{matrix}\right.\)

mà \(\left|2x-7\right|+\left|2x-5\right|=-18\)

\(\Rightarrow\)Cmin\(\Leftrightarrow\)2x-7=0 suy ra x=7/2

                2x-5=0 suy ra x=5/2

làm kiểu gì vậy

100000% đề sai còn bài làm đúng

E =16+112+120+130+142+156

E=\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}\)

 E=\(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{1}-...+\dfrac{1}{7}-\dfrac{1}{8}\)

 E=\(\dfrac{1}{2}-\dfrac{1}{8}=\dfrac{3}{8}\)