Giải thích các bước giải:
a.$\dfrac{a+b}{3}=\dfrac{b+c}{4}=\dfrac{c+a}{5}=\dfrac{a+b+b+c+c+a}{3+4+5}=\dfrac{a+b+c}{6}$
$\rightarrow \dfrac{a+b+c-a-b}{6-3}=\dfrac{a+b+c-b-c}{6-4}=\dfrac{a+b+c-c-a}{6-5}$
$\rightarrow \dfrac{c}{3}=\dfrac{a}{2}=\dfrac{b}{1}=k$
$\rightarrow c=3k, a=2k, b=k$
$\rightarrow M=-8.2k+k+5.3k+2018=2018$