$\frac{204.207+6}{205.205+209}$
= $\frac{204.(205+2)+6}{205.205+209}$
= $\frac{204.205+204.2+6}{205.205+209}$
= $\frac{204.205+204+204+6}{205.205+209}$
= $\frac{204.205+(205-1)+210}{205.205+209}$
= $\frac{205.205-1+210}{205.205+209}$
= $\frac{205.205+209}{205.205+209}$
= 1
Chúc học tốt!!!