Giải :
Đặt \(\frac{x}{2013}=\frac{y}{2014}=\frac{z}{2015}=k\Rightarrow\hept{\begin{cases}x=2013k\\y=2014k\\z=2015k\end{cases}}\)
Khi đó, ta có : 4(2013k - 2014k)(2014k - 2015k) = 4. (-k).(-k) = 4.k2 (1)
(2015k - 2013k)2 = (2k)2 = 22.k2 = 4k2 (2)
Từ (1) và (2) suy ta 4(x - y)(y - z) = (z - x)2
Heyy Mr.Kudo shinichi , thanks for helping, but I've finish already.. :<((
\(\frac{x}{2013}=\frac{y}{2014}=\frac{z}{2015}=k \)
\(\Rightarrow\hept{\begin{cases}x=2013k\\y=2014k\\z=2015k\end{cases}}\)
\(\text{Ta có :}\)
\(\text{4(x - y)(y - z) = 4(2013k - 2014k)(2014k - 2015k) }\)
=4.(-k).(-k) = 4k2 (1)
(z - x)2 = (2015k - 2013k)2 = (2k)2 = 4k2 (2)
\(\text{Từ 1 và 2}\)
=>\(\text{ 4(x - y)(y - z) = (z - x)}\)2