\(a,0,\left(123\right)+0,\left(876\right)=\dfrac{123}{999}+\dfrac{876}{999}=\dfrac{999}{999}=1\left(đpcm\right)\\ b,0,\left(123\right).3+0,\left(630\right)=\dfrac{123}{999}.3+\dfrac{630}{999}=\dfrac{369}{999}+\dfrac{630}{999}=\dfrac{999}{999}=1\left(đpcm\right)\)