b) B = 2/11. -5/4 + 9/11.-5/4 + 1 3/4

* Hướng dẫn giải

b) $\mathrm{B}=\frac{2}{11}.\frac{-5}{4}+\frac{9}{11}.\frac{-5}{4}+1\frac{3}{4}$

$$\begin{gathered} =\frac{-5}{4}.\left(\frac{2}{11}+\frac{9}{11}\right)+\frac{4.1+3}{4} \\ =\frac{-5}{4}.\left(\frac{2+9}{11}\right)+\frac{7}{4} \\ =\frac{-5}{4}.\frac{11}{11}+\frac{7}{4} \\ =\frac{-5}{4}.1+\frac{7}{4} \\ =\frac{-5+7}{4} \\ =\frac{2}{4} \\ =\frac{1}{2} \end{gathered}$$