+ \(\frac{a}{2009}=\frac{b}{2010}\Leftrightarrow2010a=2009b.\)(1)
+ \(\frac{a+2009}{a-2009}=\frac{b+2010}{b-2010}\Rightarrow\left(a+2009\right)\left(b-2010\right)=\left(a-2009\right)\left(b+2010\right)\)
\(\Rightarrow ab-2010a+2009b-2009.2010=ab+2010a-2009b-2009.2010\)
\(\Leftrightarrow2.2009.b=2.2010.a\Leftrightarrow2010a=2009b\)(2)
Từ (1) và (2) => dpcm