C=5/7.(2/11+9/11)+1.5/7
C=5/7.1+12/7
C=5/7+12/7
C=17/7
\(C=\frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+1\frac{5}{7}\)
\(C=\frac{-5}{7}.\left(\frac{2}{11}+\frac{9}{11}\right)+\frac{12}{7}\)
\(C=\frac{-5}{7}.\frac{11}{11}+\frac{12}{7}=\frac{-5}{7}.1+\frac{12}{7}=\frac{-5}{7}+\frac{12}{7}=\frac{7}{7}=1\)
Vậy C=11