`A= 2^100 - 2^99 + 2^98 - 2^97 +....+2^2 -2`
`2A =2( 2^100 - 2^99 + 2^98 - 2^97 +....+2^2 -2)`
`2A = 2^101 -2^100 + 2^99 - 2^98 +...+ 2^3 - 2^2`
`2A + A = 2^101 -2^100 + 2^99 - 2^98 +...+ 2^3 - 2^2 + 2^100 - 2^99 + 2^98 - 2^97 +....+2^2 -2`
`3A = 2^101 - 2`
`A= ( 2^101-2)/3`
Vậy `A= (2^101 -2)/3`