S1 = 1+2+$2^{2}$ +$2^{3}$ +...+ $2^{63}$
Nhân vế với 2 ta có :
2S1 = 2 + $2^{2}$ + $2^{3}$ + $2^{4}$ +.....+$2^{63}$ +$2^{64}$
2S1 - S1 = ( 2 + $2^{2}$ + $2^{3}$ + $2^{4}$ +.....+$2^{63}$ +$2^{64}$ ) - ( 1+2+$2^{2}$ +$2^{3}$ +...+ $2^{63}$ )
S1 . ( 2 - 1 ) = $2^{64}$ - 1
S1 = $2^{64}$ - 1
"Học tốt"
:>>Hạ