\(\frac{a}{2015}=\frac{b}{2016}\)
=>a=\(\frac{2015}{2016}b\)
\(\frac{b}{2016}=\frac{c}{2017}\)
=>c=\(\frac{2017}{2016}b\)
\(4.\left(a-b\right).\left(b-c\right)=4.\left(\frac{2015}{2016}b-b\right).\left(b-\frac{2017}{2016}b\right)=4.\frac{-1}{2016}b.\frac{-1}{2016}b=\frac{1}{1016064}b^2\)
\(\left(c-a\right)^2=\left(\frac{2017}{2016}b-\frac{2015}{2016}b\right)^2=\left(\frac{1}{1008}b\right)^2=\frac{1}{1016064}b^2\)
=>ĐPCM