Tính: b) ( − 7/17 ) . 5/12 + ( − 7/17 ) . 7/12 + ( − 10/17 ) ;

b) $\left(\frac{-7}{17}\right).\frac{5}{12}+\left(\frac{-7}{17}\right).\frac{7}{12}+\left(\frac{-10}{17}\right)$

$=\left(\frac{-7}{17}\right).(\frac{5}{12}+\frac{7}{12})+\left(\frac{-10}{17}\right)$

$=\left(\frac{-7}{17}\right).1+\left(\frac{-10}{17}\right)=\left(\frac{-7}{17}\right)+\left(\frac{-10}{17}\right)$

$=\frac{-17}{17}=-1$