Bài 1: Ta có:
\(\dfrac{a+2009}{a-2009}=\dfrac{b+2010}{b-2010}\Rightarrow\left(a+2009\right)\left(b-2010\right)=\left(a-2009\right)\left(b+2010\right)\\ \Leftrightarrow ab-2010a+2009b-4038090=ab+2010a-2009b-4038090\\ \Leftrightarrow-2010a+2009b=2010a-2009b\\ \Leftrightarrow4018b=4020a\\ \Leftrightarrow1009b=1010a\\ \Leftrightarrow\dfrac{a}{2009}=\dfrac{b}{2010}\left(dpcm\right)\)