Ta có :
\(\left(\frac{2006-2005}{2006+2005}\right)^2=\frac{\left(2006-2005\right)^2}{\left(2006+2005\right)^2}=\frac{2006^2-2.2006.2005+2005^2}{2006^2+2.2006.2005+2005^2}=\frac{2006^2-2005^2}{2006^2+2005^2}\)
Vậy \(\left(\frac{2006-2005}{2006+2005}\right)^2=\frac{2006^2-2005^2}{2006^2+2005^2}\)