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`
Giải thích các bước giải:
