$ 30 A = \dfrac{30^{9} + 30}{30^9+1} = \dfrac{30^{9} + 1+ 29}{30^9+1} $
$ = \dfrac{30^{9} + 1}{30^9+1} + \dfrac{29}{30^9+1} = 1 + \dfrac{29}{30^9+1} $
$30B = \dfrac{30^{10} + 30}{30^{10}+1} = \dfrac{30^{10} + 1+ 29}{30^{10}+1} $
$ = \dfrac{30^{10} + 1}{30^{10}+1} + \dfrac{29}{30^{10}+1} = 1 + \dfrac{29}{30^{10}+1} $
Ta có $ 30^9 +1 < 30^{10} +1 \to \dfrac{29}{30^9+1} > \dfrac{29}{30^{10}+1} $
$\to 1 + \dfrac{29}{30^9+1} > 1 + \dfrac{29}{30^{10}+1} $
$\to 30A > 30B$
$\to A >B$
