Đáp án:
`A=1`
Giải thích các bước giải:
`A=4*|\underbrace{-1/3+1/3^2+(-1/3^3)+....+1/3^100}_{B}|+1/3^100`
`A=|4.\underbrace{-1/3+1/3^2+(-1/3^3)+....+1/3^100}_{B}|+1/3^100`
`3B=-1+1/3-1/3^2+....+1/3^99`
`=>3B+B=-1+1/3^100`
`=>4B==-1+1/3^100`
`=>A=|-1+1/3^100|+1/3^100`
`A=1-1/3^100+1/3^100`(do `1>1/3^100`)
`A=1`