211.13+213.15+....+297.99211.13+213.15+....+297.99
=111−113+113−115+....+197−199=111-113+113-115+....+197-199
=111−199=899
\(\dfrac{2}{13x}=-\dfrac{4}{13}\Rightarrow\dfrac{2}{x}=-4\Rightarrow-4x=2\Rightarrow x=-\dfrac{1}{2}\)
Ta có: \(\dfrac{2}{13}\cdot x=\dfrac{-4}{13}\)
\(\Leftrightarrow x=\dfrac{-4}{13}:\dfrac{2}{13}=\dfrac{-4}{13}\cdot\dfrac{13}{2}=-2\)
\(\dfrac{2}{13}.x=\dfrac{-4}{13}\)
\(\Leftrightarrow x=\dfrac{-4}{13}.\dfrac{13}{2}\)
\(\Leftrightarrow x=-2\)
\(\dfrac{2}{13}.x=\dfrac{-4}{13}\)
\(x=\dfrac{-4}{13}:\dfrac{2}{13}\)
\(x=-2\)
\(\dfrac{2}{13}x=\dfrac{-4}{13}\)
<=> 2x = -4
<=> x = -2
