`+)`
`C=4+1/7^6 + 3/7+4/7^2+(-441)/7^6+(27)/7^5`
`C=4+1/7^6+3/7+4/7^2+(-9/7^4)+(27)/(7^5)`
`C=(4+3/7+4/7^2+(27)/7^5)+(-9/7^4+1/7^6)`
`+)`
`D=(147)/7^3+4+(35)/7^7+4/(7^2)+(27)/(7^5)+(-9/7^9)`
`D=3/7+4+5/7^6+4/7^2+(27)/7^5+(-9/7^9)`
`D=(4+3/7+4/7^2+(27)/7^5)+(-9/7^9+5/7^6)`
Ta có:
`-9/7^4+1/7^6 < -9/7^9+5/7^6`
`⇒(4+3/7+4/7^2+(27)/7^5)+(-9/7^4+1/7^6) < (4+3/7+4/7^2+(27)/7^5)+(-9/7^9+5/7^6)`
`⇒C < D`