So sánh A=(〖19〗^30+5)/(〖19〗^31+5) và B=(〖19〗^31+5)/(〖19〗^32+5)

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1. A=19^30+5/19^31+5

   ⇔19A=19^31+5+90/19^31+5

   ⇔19A=1+ 90/19^31 +5

   B=19^31+5/19^32+5

   ⇔19B=19^32+5+90/19^32+5
   ⇔19B=1+ 90/19^32 +5

   vì 90/19^31 > 90/19^32

   ⇒ A>B

   xin ctlhn

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2. Ta có:

   $A = \dfrac{19^{30} + 5}{19^{31}+5}$

   $⇔19A = \dfrac{19^{31} + 95}{19^{31} + 5}$

   $⇔ 19A = \dfrac{19^{31} + 5 + 90}{19^{31} + 5}$

   $⇔ 19A = 1 + \dfrac{90}{19^{31} + 5}$

   $B = \dfrac{19^{31} + 5}{19^{32}+5}$

   $⇔19B = \dfrac{19^{32} + 95}{19^{32} + 5}$

   $⇔ 19B = \dfrac{19^{32} + 5 + 90}{19^{32} + 5}$

   $⇔ 19B = 1 + \dfrac{90}{19^{32} + 5}$

    Vì : $\dfrac{90}{19^{31} + 5} > \dfrac{90}{19^{32} + 5}$

   $→ A > B$.

    

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