$\dfrac{-3}{40}$ + $\dfrac{-3}{88}$ + $\dfrac{-3}{154}$ + $\dfrac{-3}{238}$ + $\dfrac{-3}{340}$ + $\dfrac{-3}{460}$
=$\dfrac{-90321}{1204280}$ + $\dfrac{-41055}{1204280}$ + $\dfrac{-23460}{1204280}$ + $\dfrac{-15180}{1204280}$ + $\dfrac{-10626}{1204280}$ + $\dfrac{-7854}{1204280}$
= -$\dfrac{188496}{1204280}$
= -$\dfrac{18}{115}$
xin hay nhất ạ