rút gọn B=25^5+25^7+25^9:5^11+5^13+5^15+5^17+5^17+5^19+5^21

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1. `B=(25^5+25^7+25^9)/(5^11+5^13+5^15+5^17+5^19+5^21)`

   `->B=((5^2)^5+(5^2)^7+(5^2)^9)/(5^10 .5+5^10 .5^3+5^10 .5^5+5^10 .5^7+5^10 .5^9+5^10 .5^11)`

   `->B=(5^10+5^14+5^18)/(5^10(5+5^3+5^5+5^7+5^9+5^11))` 

   `->B=(5^10+5^10 .5^4+5^10 .5^8)/(5^10(5+5^3+5^5+5^7+5^9+5^11))`

   `->B=(5^10(1+5^4+5^8))/(5^10(5+5^3+5^5+5^7+5^9+5^11)`

   `->B=(1+5^4+5^8)/(5+5^3+5^5+5^7+5^9+5^11)`

   `->B=(1+5^4+5^8)/((5+5^5+5^9)+(5^3+5^7+5^11))`

   `->B=(1+5^4+5^8)/((5+5^4 .5+5^8 .5)+(5^3+5^4 .5^3+5^8 .5^3))`

   `->B=(1+5^4+5^8)/(5(1+5^4+5^8)+5^3(1+5^4+5^8))`

   `->B=(1+5^4+5^8)/((1+5^4+5^8)(5+5^3)`

   `->B=1/(5+5^3)`

   `->B=1/(5+125)`

   `->B=1/130`

   – Vậy `B=1/130`

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2. Đáp án:

    Ta có :

   `B=(25^5+25^7+25^9)/(5^11+5^13+5^15+5^17+5^19+5^21)`

   `=>B=((5^2)^5+(5^2)^7+(5^2)^9)/(5^10 .5+5^10 .5^3+5^10 .5^5+5^10 .5^7+5^10 .5^9+5^10 .5^11)`

   `=>B=(5^10+5^14+5^18)/(5^10(5+5^3+5^5+5^7+5^9+5^11))`

   `=>B=(5^10+5^10 .5^4+5^10 .5^8)/(5^10(5+5^3+5^5+5^7+5^9+5^11))`

   `=>B=(5^10(1+5^4+5^8))/(5^10(5+5^3+5^5+5^7+5^9+5^11)`

   `=>B=(1+5^4+5^8)/(5+5^3+5^5+5^7+5^9+5^11)`

   `=>B=(1+5^4+5^8)/((5+5^5+5^9)+(5^3+5^7+5^11))`

   `=>B=(1+5^4+5^8)/((5+5^4 .5+5^8 .5)+(5^3+5^4 .5^3+5^8 .5^3))`

   `=>B=(1+5^4+5^8)/(5(1+5^4+5^8)+5^3(1+5^4+5^8))`

   `=>B=(1+5^4+5^8)/((1+5^4+5^8)(5+5^3)`

   `=>B=1/(5+5^3)`

   `=>B=1/(5+125)`

   `=>B=1/130`

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